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SynonymsPneumonitis, bronchopneumonia [1]
Chest radiograph in influensa and H influenzae, posteroanterior, annotated.jpg
Chest X-ray of a pneumonia caused by influenza and Haemophilus influenzae , with patchy consolidations, mainly in the right upper lobe (arrow).
Specialty Pulmonology, Infectious disease
SymptomsCough, difficulty breathing, rapid breathing, fever [2]
DurationFew weeks [3]
CausesBacteria, virus, aspiration [4] [5]
Risk factors Cystic fibrosis, COPD, asthma, diabetes, heart failure, history of smoking [6]
Diagnostic method Based on symptoms, chest X-ray [7]
Differential diagnosis COPD, asthma, pulmonary edema, pulmonary embolism [8]
Prevention Vaccines, handwashing, not smoking [9]
Medication Antibiotics, antivirals, oxygen therapy [10] [11]
Frequency450 million (7%) per year [11] [12]
Deaths4 million per year [11] [12]

Pneumonia is an inflammatory condition of the lung affecting primarily the small air sacs known as alveoli. [4] [13] Typically symptoms include some combination of productive or dry cough, chest pain, fever, and trouble breathing. [2] Severity is variable. [2]

Inflammation signs of activation of the immune system

Inflammation is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molecular mediators. The function of inflammation is to eliminate the initial cause of cell injury, clear out necrotic cells and tissues damaged from the original insult and the inflammatory process, and initiate tissue repair.

Lung essential respiration organ in many air-breathing animals

The lungs are the primary organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their function in the respiratory system is to extract oxygen from the atmosphere and transfer it into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange. Respiration is driven by different muscular systems in different species. Mammals, reptiles and birds use their different muscles to support and foster breathing. In early tetrapods, air was driven into the lungs by the pharyngeal muscles via buccal pumping, a mechanism still seen in amphibians. In humans, the main muscle of respiration that drives breathing is the diaphragm. The lungs also provide airflow that makes vocal sounds including human speech possible.

Phlegm is a liquid secreted by the mucous membranes of mammals. Its definition is limited to the mucus produced by the respiratory system, excluding that from the nasal passages, and particularly that which is expelled by coughing (sputum). Phlegm is in essence a water-based gel consisting of glycoproteins, immunoglobulins, lipids and other substances. Its composition varies depending on climate, genetics, and state of the immune system. Its color can vary from transparent to pale or dark yellow and green, from light to dark brown, and even to dark grey depending on the constituents.


Pneumonia is usually caused by infection with viruses or bacteria and less commonly by other microorganisms, certain medications and conditions such as autoimmune diseases. [4] [5] Risk factors include other lung diseases such as cystic fibrosis, COPD, and asthma, diabetes, heart failure, a history of smoking, a poor ability to cough such as following a stroke, or a weak immune system. [6] Diagnosis is often based on the symptoms and physical examination. [7] Chest X-ray, blood tests, and culture of the sputum may help confirm the diagnosis. [7] The disease may be classified by where it was acquired with community, hospital, or health care associated pneumonia. [14]

Virus Type of non-cellular infectious agent

A virus is a small infectious agent that replicates only inside the living cells of an organism. Viruses can infect all types of life forms, from animals and plants to microorganisms, including bacteria and archaea.

Bacteria A domain of prokaryotes – single celled organisms without a nucleus

Bacteria are a type of biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, and are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springs, radioactive waste, and the deep portions of Earth's crust. Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only about half of the bacterial phyla have species that can be grown in the laboratory. The study of bacteria is known as bacteriology, a branch of microbiology.

Microorganism microscopic living organism

A microorganism, or microbe, is a microscopic organism, which may exist in its single-celled form or in a colony of cells.

Vaccines to prevent certain types of pneumonia are available. [9] Other methods of prevention include handwashing and not smoking. [9] Treatment depends on the underlying cause. [15] Pneumonia believed to be due to bacteria is treated with antibiotics. [10] If the pneumonia is severe, the affected person is generally hospitalized. [15] Oxygen therapy may be used if oxygen levels are low. [10]

Vaccine biological preparatory medicine that improves immunity to a particular disease

A vaccine is a biological preparation that provides active acquired immunity to a particular disease. A vaccine typically contains an agent that resembles a disease-causing microorganism and is often made from weakened or killed forms of the microbe, its toxins, or one of its surface proteins. The agent stimulates the body's immune system to recognize the agent as a threat, destroy it, and to further recognize and destroy any of the microorganisms associated with that agent that it may encounter in the future. Vaccines can be prophylactic, or therapeutic.

Antibiotic drug used in the treatment and prevention of bacterial infections

An antibiotic is a type of antimicrobial substance active against bacteria and is the most important type of antibacterial agent for fighting bacterial infections. Antibiotic medications are widely used in the treatment and prevention of such infections. They may either kill or inhibit the growth of bacteria. A limited number of antibiotics also possess antiprotozoal activity. Antibiotics are not effective against viruses such as the common cold or influenza; drugs which inhibit viruses are termed antiviral drugs or antivirals rather than antibiotics.

Oxygen therapy Use of high inhalation concentrations of oxygen as medical treatment

Oxygen therapy, also known as supplemental oxygen, is the use of oxygen as a medical treatment. This can include for low blood oxygen, carbon monoxide toxicity, cluster headaches, and to maintain enough oxygen while inhaled anesthetics are given. Long-term oxygen is often useful in people with chronically low oxygen such as from severe COPD or cystic fibrosis. Oxygen can be given in a number of ways including nasal cannula, face mask, and inside a hyperbaric chamber.

Pneumonia affects approximately 450 million people globally (7% of the population) and results in about 4 million deaths per year. [11] [12] Pneumonia was regarded by William Osler in the 19th century as "the captain of the men of death". [16] With the introduction of antibiotics and vaccines in the 20th century, survival improved. [11] Nevertheless, in developing countries, and among the very old, the very young, and the chronically ill, pneumonia remains a leading cause of death. [11] [17] Pneumonia often shortens suffering among those already close to death and has thus been called "the old man's friend". [18]

William Osler Canadian pathologist, physician, educator, bibliophile, historian, author, cofounder of Johns Hopkins Hospital

Sir William Osler, 1st Baronet, was a Canadian physician and one of the four founding professors of Johns Hopkins Hospital. Osler created the first residency program for specialty training of physicians, and he was the first to bring medical students out of the lecture hall for bedside clinical training. He has frequently been described as the Father of Modern Medicine and one of the "greatest diagnosticians ever to wield a stethoscope". Osler was a person of many interests, who in addition to being a physician, was a bibliophile, historian, author, and renowned practical joker. One of his achievements was the founding of the History of Medicine Society of the Royal Society of Medicine, London.

Video summary (script)

Signs and symptoms

Symptoms frequency [19]
Shortness of breath67–75%
Chest pain39–49%
Main symptoms of infectious pneumonia Symptoms of pneumonia.svg
Main symptoms of infectious pneumonia

People with infectious pneumonia often have a productive cough, fever accompanied by shaking chills, shortness of breath, sharp or stabbing chest pain during deep breaths, and an increased rate of breathing. [8] In elderly people, confusion may be the most prominent sign. [8]

Cough medical symptom, reflex to clear large breathing passages

A cough is a sudden, and often repetitively occurring, protective reflex which helps to clear the large breathing passages from fluids, irritants, foreign particles and microbes. The cough reflex consists of three phases: an inhalation, a forced exhalation against a closed glottis, and a violent release of air from the lungs following opening of the glottis, usually accompanied by a distinctive sound.

Fever common medical sign characterized by elevated body temperature

Fever, also known as pyrexia and febrile response, is defined as having a temperature above the normal range due to an increase in the body's temperature set point. There is not a single agreed-upon upper limit for normal temperature with sources using values between 37.5 and 38.3 °C. The increase in set point triggers increased muscle contractions and causes a feeling of cold. This results in greater heat production and efforts to conserve heat. When the set point temperature returns to normal, a person feels hot, becomes flushed, and may begin to sweat. Rarely a fever may trigger a febrile seizure. This is more common in young children. Fevers do not typically go higher than 41 to 42 °C.

Shortness of breath, also known as dyspnea, is the feeling that one cannot breathe well enough. The American Thoracic Society defines it as "a subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity", and recommends evaluating dyspnea by assessing the intensity of the distinct sensations, the degree of distress involved, and its burden or impact on activities of daily living. Distinct sensations include effort/work, chest tightness, and air hunger.

The typical signs and symptoms in children under five are fever, cough, and fast or difficult breathing. [20] Fever is not very specific, as it occurs in many other common illnesses and may be absent in those with severe disease, malnutrition or in the elderly. In addition, a cough is frequently absent in children less than 2 months old. [20] More severe signs and symptoms in children may include blue-tinged skin, unwillingness to drink, convulsions, ongoing vomiting, extremes of temperature, or a decreased level of consciousness. [20] [21]

Malnutrition Medical condition that results from eating too little, too much, or the wrong nutrients

Malnutrition is a condition that results from eating a diet in which one or more nutrients are either not enough or are too much such that the diet causes health problems. It may involve calories, protein, carbohydrates, vitamins or minerals. Not enough nutrients is called undernutrition or undernourishment while too much is called overnutrition. Malnutrition is often used to specifically refer to undernutrition where an individual is not getting enough calories, protein, or micronutrients. If undernutrition occurs during pregnancy, or before two years of age, it may result in permanent problems with physical and mental development. Extreme undernourishment, known as starvation, may have symptoms that include: a short height, thin body, very poor energy levels, and swollen legs and abdomen. People also often get infections and are frequently cold. The symptoms of micronutrient deficiencies depend on the micronutrient that is lacking.

Bacterial and viral cases of pneumonia usually result in similar symptoms. [22] Some causes are associated with classic, but non-specific, clinical characteristics. Pneumonia caused by Legionella may occur with abdominal pain, diarrhea, or confusion. [23] Pneumonia caused by Streptococcus pneumoniae is associated with rusty colored sputum. [24] Pneumonia caused by Klebsiella may have bloody sputum often described as "currant jelly". [19] Bloody sputum (known as hemoptysis) may also occur with tuberculosis, Gram-negative pneumonia, lung abscesses and more commonly acute bronchitis. [21] Pneumonia caused by Mycoplasma pneumoniae may occur in association with swelling of the lymph nodes in the neck, joint pain, or a middle ear infection. [21] Viral pneumonia presents more commonly with wheezing than bacterial pneumonia. [22] Pneumonia was historically divided into "typical" and "atypical" based on the belief that the presentation predicted the underlying cause. [25] However, evidence has not supported this distinction, therefore it is no longer emphasized. [25]


The bacterium Streptococcus pneumoniae, a common cause of pneumonia, imaged by an electron microscope Streptococcus pneumoniae.jpg
The bacterium Streptococcus pneumoniae , a common cause of pneumonia, imaged by an electron microscope

Pneumonia is due to infections caused primarily by bacteria or viruses and less commonly by fungi and parasites. Although there are over 100 strains of infectious agents identified, only a few are responsible for the majority of the cases. Mixed infections with both viruses and bacteria may occur in roughly 45% of infections in children and 15% of infections in adults. [11] A causative agent may not be isolated in approximately half of cases despite careful testing. [18]

The term pneumonia is sometimes more broadly applied to any condition resulting in inflammation of the lungs (caused for example by autoimmune diseases, chemical burns or drug reactions); however, this inflammation is more accurately referred to as pneumonitis. [26] [27]

Factors that predispose to pneumonia include smoking, immunodeficiency, alcoholism, chronic obstructive pulmonary disease, asthma, chronic kidney disease, liver disease, and old age. [21] [28] Additional risk in children include not being breastfeed, exposure to cigarettes or air pollution, malnutrition, and poverty. [29] The use of acid-suppressing medications – such as proton-pump inhibitors or H2 blockers – is associated with an increased risk of pneumonia. [30] Approximately 10% of people who require mechanical ventilation develop ventilator associated pneumonia, [31] and people with gastric feeding tube have an increased risk of developing of aspiration pneumonia. [32] For people with specific variants of FER gene, the risk of death is reduced in sepsis caused by pneumonia. However, for those with TLR6 variants, the risk of getting Legionnaires' disease is increased. [33]


Cavitating pneumonia as seen on CT. Pneumonia due to MRSA. MRSAPneumoCT.png
Cavitating pneumonia as seen on CT. Pneumonia due to MRSA.

Bacteria are the most-common cause of community-acquired pneumonia (CAP), with Streptococcus pneumoniae isolated in nearly 50% of cases. [34] [35] Other commonly-isolated bacteria include Haemophilus influenzae in 20%, Chlamydophila pneumoniae in 13%, and Mycoplasma pneumoniae in 3% of cases; [34] Staphylococcus aureus ; Moraxella catarrhalis ; Legionella pneumophila ; and Gram-negative bacilli. [18] A number of drug-resistant versions of the above infections are becoming more common, including drug-resistant Streptococcus pneumoniae (DRSP) and methicillin-resistant Staphylococcus aureus (MRSA). [21]

The spreading of organisms is facilitated when risk factors are present. [18] Alcoholism is associated with Streptococcus pneumoniae, anaerobic organisms, and Mycobacterium tuberculosis; smoking facilitates the effects of Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and Legionella pneumophila. Exposure to birds is associated with Chlamydia psittaci ; farm animals with Coxiella burnetti ; aspiration of stomach contents with anaerobic organisms; and cystic fibrosis with Pseudomonas aeruginosa and Staphylococcus aureus. [18] Streptococcus pneumoniae is more common in the winter, [18] and it should be suspected in persons aspirating a large amount of anaerobic organisms. [21]


In adults, viruses account for approximately a third [11] and in children for about 15% of pneumonia cases. [36] Commonly-implicated agents include rhinoviruses, coronaviruses, influenza virus, respiratory syncytial virus (RSV), adenovirus, and parainfluenza. [11] [37] Herpes simplex virus rarely causes pneumonia, except in groups such as: newborns, persons with cancer, transplant recipients, and people with significant burns. [38] People following organ transplantation or those otherwise-immunocompromised present high rates of cytomegalovirus pneumonia. [36] [38] Those with viral infections may be secondarily infected with the bacteria Streptococcus pneumoniae, Staphylococcus aureus, or Haemophilus influenzae, particularly when other health problems are present. [21] [36] Different viruses predominate at different periods of the year; during flu season, for example, influenza may account for over half of all viral cases. [36] Outbreaks of other viruses also occasionally occur, including hantaviruses and coronavirus . [36]


Fungal pneumonia is uncommon, but occurs more commonly in individuals with weakened immune systems due to AIDS, immunosuppressive drugs, or other medical problems. [18] [39] It is most often caused by Histoplasma capsulatum , blastomyces, Cryptococcus neoformans , Pneumocystis jiroveci (pneumocystis pneumonia, or PCP), and Coccidioides immitis . Histoplasmosis is most common in the Mississippi River basin, and coccidioidomycosis is most common in the Southwestern United States. [18] The number of cases has been increasing in the later half of the 20th century due to increasing travel and rates of immunosuppression in the population. [39] For people infected with HIV/AIDS, PCP is a common opportunistic infection. [40]


A variety of parasites can affect the lungs, including Toxoplasma gondii , Strongyloides stercoralis , Ascaris lumbricoides , and Plasmodium malariae . [41] These organisms typically enter the body through direct contact with the skin, ingestion, or via an insect vector. [41] Except for Paragonimus westermani , most parasites do not affect specifically the lungs but involve the lungs secondarily to other sites. [41] Some parasites, in particular those belonging to the Ascaris and Strongyloides genera, stimulate a strong eosinophilic reaction, which may result in eosinophilic pneumonia. [41] In other infections, such as malaria, lung involvement is due primarily to cytokine-induced systemic inflammation. [41] In the developed world these infections are most common in people returning from travel or in immigrants. [41] Around the world, these infections are most common in the immunodeficient. [42]


Idiopathic interstitial pneumonia or noninfectious pneumonia [43] is a class of diffuse lung diseases. They include diffuse alveolar damage, organizing pneumonia, nonspecific interstitial pneumonia, lymphocytic interstitial pneumonia, desquamative interstitial pneumonia, respiratory bronchiolitis interstitial lung disease, and usual interstitial pneumonia. [44] Lipoid pneumonia is another rare cause due to lipids entering the lung. [45] These lipids can either be inhaled or from lipids within the body. [45]


Pneumonia fills the lung's alveoli with fluid, hindering oxygenation. The alveolus on the left is normal, whereas the one on the right is full of fluid from pneumonia. New Pneumonia cartoon.jpg
Pneumonia fills the lung's alveoli with fluid, hindering oxygenation. The alveolus on the left is normal, whereas the one on the right is full of fluid from pneumonia.

Pneumonia frequently starts as an upper respiratory tract infection that moves into the lower respiratory tract. [46] It is a type of pneumonitis (lung inflammation). [47] The normal flora of the upper airway gives protection by competing with pathogens for nutrients. In the lower airways, reflexes of the glottis, actions of complement proteins and immunoglobulins are important for protection. Microaspiration of contaminated secretions can infect the lower airways and cause pneumonia. The virulence of the organism, amount of the organisms to start an infection and body immune response against the infection all determines the progress of pneumonia. [33]


Most bacteria enter the lungs via small aspirations of organisms residing in the throat or nose. [21] Half of normal people have these small aspirations during sleep. [25] While the throat always contains bacteria, potentially infectious ones reside there only at certain times and under certain conditions. [25] A minority of types of bacteria such as Mycobacterium tuberculosis and Legionella pneumophila reach the lungs via contaminated airborne droplets. [21] Bacteria can spread also via the blood. [22] Once in the lungs, bacteria may invade the spaces between cells and between alveoli, where the macrophages and neutrophils (defensive white blood cells) attempt to inactivate the bacteria. [48] The neutrophils also release cytokines, causing a general activation of the immune system. [49] This leads to the fever, chills, and fatigue common in bacterial pneumonia. [49] The neutrophils, bacteria, and fluid from surrounding blood vessels fill the alveoli, resulting in the consolidation seen on chest X-ray. [50]


Viruses may reach the lung by a number of different routes. Respiratory syncytial virus is typically contracted when people touch contaminated objects and then they touch their eyes or nose. [36] Other viral infections occur when contaminated airborne droplets are inhaled through the mouth or nose. [21] Once in the upper airway, the viruses may make their way in the lungs, where they invade the cells lining the airways, alveoli, or lung parenchyma. [36] Some viruses such as measles and herpes simplex may reach the lungs via the blood. [51] The invasion of the lungs may lead to varying degrees of cell death. [36] When the immune system responds to the infection, even more lung damage may occur. [36] Primarily white blood cells, mainly mononuclear cells, generate the inflammation. [51] As well as damaging the lungs, many viruses simultaneously affect other organs and thus disrupt other body functions. Viruses also make the body more susceptible to bacterial infections; in this way, bacterial pneumonia can occur at the same time as viral pneumonia. [37]


Pneumonia is typically diagnosed based on a combination of physical signs and a chest X-ray. [52] However, the underlying cause can be difficult to confirm, as there is no definitive test able to distinguish between bacterial and non-bacterial origin. [11] [52]

The World Health Organization has defined pneumonia in children clinically based on either a cough or difficulty breathing and a rapid respiratory rate, chest indrawing, or a decreased level of consciousness. [53] A rapid respiratory rate is defined as greater than 60 breaths per minute in children under 2 months old, greater than 50 breaths per minute in children 2 months to 1 year old, or greater than 40 breaths per minute in children 1 to 5 years old. [53] In children, low oxygen levels and lower chest indrawing are more sensitive than hearing chest crackles with a stethoscope or increased respiratory rate. [54] Grunting and nasal flaring may be other useful signs in children less than five years old. [55] Lack of wheezing is an indicator of Mycoplasma pneumoniae in children with pneumonia, but as an indicator it is not accurate enough to decide whether or not macrolide treatment should be used. [56] The presence of chest pain in children with pneumonia doubles the probability of Mycoplasma pneumoniae. [56]

In general, in adults, investigations are not needed in mild cases. [57] There is a very low risk of pneumonia if all vital signs and auscultation are normal. [58] In persons requiring hospitalization, pulse oximetry, chest radiography and blood tests – including a complete blood count, serum electrolytes, C-reactive protein level, and possibly liver function tests – are recommended. [57] Procalcitonin may help determine the cause and support who should receive antibiotics. [59] Antibiotics is encouraged if procalcitonin level reaches 0.25 μg/L, strongly encouraged if it reaches 0.5 μg/L, and strongly discouraged if the level is below 0.10 μg/L. [33] For those with CRP less than 20 mg/L without convincing evidence of pneumonia, antibiotics are not recommended. [33]

The diagnosis of influenza-like illness can be made based on the signs and symptoms; however, confirmation of an influenza infection requires testing. [60] Thus, treatment is frequently based on the presence of influenza in the community or a rapid influenza test. [60]

Physical exam

Physical examination may sometimes reveal low blood pressure, high heart rate, or low oxygen saturation. [21] The respiratory rate may be faster than normal, and this may occur a day or two before other signs. [21] [25] Examination of the chest may be normal, but it may show decreased chest expansion on the affected side. Harsh breath sounds from the larger airways that are transmitted through the inflamed lung are termed bronchial breathing and are heard on auscultation with a stethoscope. [21] Crackles (rales) may be heard over the affected area during inspiration. [21] Percussion may be dulled over the affected lung, and increased, rather than decreased, vocal resonance distinguishes pneumonia from a pleural effusion. [8]


A chest X-ray showing a very prominent wedge-shape area of airspace consolidation in the right lung characteristic of acute bacterial lobar pneumonia X-ray of lobar pneumonia.jpg
A chest X-ray showing a very prominent wedge-shape area of airspace consolidation in the right lung characteristic of acute bacterial lobar pneumonia
CT of the chest demonstrating right-side pneumonia (left side of the image) CT scan of the chest, demonstrating right-sided pneumonia.jpg
CT of the chest demonstrating right-side pneumonia (left side of the image)

A chest radiograph is frequently used in diagnosis. [20] In people with mild disease, imaging is needed only in those with potential complications, those not having improved with treatment, or those in which the cause is uncertain. [20] [57] If a person is sufficiently sick to require hospitalization, a chest radiograph is recommended. [57] Findings do not always match the severity of disease and do not reliably separate between bacterial infection and viral infection. [20]

X-ray presentations of pneumonia may be classified as lobar pneumonia, bronchopneumonia (also known as lobular pneumonia), and interstitial pneumonia. [61] Bacterial, community-acquired pneumonia classically show lung consolidation of one lung segmental lobe, which is known as lobar pneumonia. [34] However, findings may vary, and other patterns are common in other types of pneumonia. [34] Aspiration pneumonia may present with bilateral opacities primarily in the bases of the lungs and on the right side. [34] Radiographs of viral pneumonia may appear normal, appear hyper-inflated, have bilateral patchy areas, or present similar to bacterial pneumonia with lobar consolidation. [34] Radiologic findings may not be present in the early stages of the disease, especially in the presence of dehydration, or may be difficult to be interpreted in the obese or those with a history of lung disease. [21] Complications such as pleural effusion may also be found on chest radiographs. Laterolateral chest radiograph can increase the diagnostic accuracy of lung consolidation and pleural effusion. [33] A CT scan can give additional information in indeterminate cases. [34] CT scan can also provide more details in those with an unclear chest radiograph (for example occult pneumonia in chronic obstructive pulmonary disease (COPD)) and is able to exclude pulmonary embolism and fungal pneumonia and detecting lung abscess in those who are not responding to treatments. [33] However, CT scan is more expensive, has a higher dose of radiation, and cannot be done at bedside. [33]

Lung ultrasound may also be useful in helping to make the diagnosis. [62] Ultrasound is radiation free and can be done at bedside. However, ultrasound requires specific skills to operate the machine and interpret the findings. [33] It may be more accurate than chest X-ray. [63]


In people managed in the community, determining the causative agent is not cost-effective and typically does not alter management. [20] For people who do not respond to treatment, sputum culture should be considered, and culture for Mycobacterium tuberculosis should be carried out in persons with a chronic productive cough. [57] Microbiological evaluation is also indicated in severe pneumonia, alcoholism, asplenia, immunosuppression, HIV infection, and alcohol abuse. [33] Although positive blood culture and pleural fluid culture definitively establish the diagnosis of the type of micro-organism involved, a positive sputum culture has to be interpreted with care for the possibility of colonisation of respiratory tract. [33] Testing for other specific organisms may be recommended during outbreaks, for public health reasons. [57] In those hospitalized for severe disease, both sputum and blood cultures are recommended, [57] as well as testing the urine for antigens to Legionella and Streptococcus. [65] Viral infections, can be confirmed via detection of either the virus or its antigens with culture or polymerase chain reaction (PCR), among other techniques. [11] Mycoplasma, Legionella, Streptococcus, and Chlamydia can also be detected using PCR techniques on bronchoalveolar lavage and nasopharyngeal swab. [33] The causative agent is determined in only 15% of cases with routine microbiological tests. [8]


Pneumonitis refers to lung inflammation; pneumonia refers to pneumonitis, usually due to infection but sometimes non-infectious, that has the additional feature of pulmonary consolidation. [66] Pneumonia is most commonly classified by where or how it was acquired: community-acquired, aspiration, healthcare-associated, hospital-acquired, and ventilator-associated pneumonia. [34] It may also be classified by the area of lung affected: lobar pneumonia, bronchial pneumonia and acute interstitial pneumonia; [34] or by the causative organism. [67] Pneumonia in children may additionally be classified based on signs and symptoms as non-severe, severe, or very severe. [68]

The setting in which pneumonia develops is important to treatment, [69] [70] as it correlates to which pathogens are likely suspects, [69] which mechanisms are likely, which antibiotics are likely to work or fail, [69] and which complications can be expected based on the person's health status.


Community-acquired pneumonia (CAP) is acquired in the community, [69] [70] outside of health care facilities. Compared with health care–associated pneumonia, it is less likely to involve multidrug-resistant bacteria. Although the latter are no longer rare in CAP, [69] they are still less likely.


Health care–associated pneumonia (HCAP) is an infection associated with recent exposure to the health care system, [69] including hospital, outpatient clinic, nursing home, dialysis center, chemotherapy treatment, or home care. [70] HCAP is sometimes called MCAP (medical care–associated pneumonia).


Hospital-acquired pneumonia is acquired in a hospital, specifically, pneumonia that occurs 48 hours or more after admission, which was not incubating at the time of admission. [70] [69] It is likely to involve hospital-acquired infections, with higher risk of multidrug-resistant pathogens. Also, because hospital people are often ill (which is why they are present in the hospital), accompanying disorders are an issue.


Ventilator-associated pneumonia occurs in people breathing with the help of mechanical ventilation. [69] [31] Ventilator-associated pneumonia is specifically defined as pneumonia that arises more than 48 to 72 hours after endotracheal intubation. [70]

Differential diagnosis

Several diseases can present with similar signs and symptoms to pneumonia, such as: chronic obstructive pulmonary disease (COPD), asthma, pulmonary edema, bronchiectasis, lung cancer, and pulmonary emboli. [8] Unlike pneumonia, asthma and COPD typically present with wheezing, pulmonary edema presents with an abnormal electrocardiogram, cancer and bronchiectasis present with a cough of longer duration, and pulmonary emboli presents with acute onset sharp chest pain and shortness of breath. [8] Mild pneumonia should be differentiated from upper respiratory tract infection (URTI). Severe pneumonia should be differentiated from acute heart failure. Pulmonary infiltrates that resolved after giving mechanical ventilation should point to heart failure and atelectasis rather than pneumonia. For recurrent pneumonia, underlying lung cancer, metastasis, tuberculosis, foreign body, immunosuppression, and hypersensitivity should be sought after. [33]


Prevention includes vaccination, environmental measures and appropriate treatment of other health problems. [20] It is believed that, if appropriate preventive measures were instituted globally, mortality among children could be reduced by 400,000; and, if proper treatment were universally available, childhood deaths could be decreased by another 600,000. [22]


Vaccination prevents against certain bacterial and viral pneumonias both in children and adults. Influenza vaccines are modestly effective at preventing symptoms of influenza, [11] [71] [ needs update ] The Center for Disease Control and Prevention (CDC) recommends yearly influenza vaccination for every person 6 months and older. [72] Immunizing health care workers decreases the risk of viral pneumonia among their people. [65]

Vaccinations against Haemophilus influenzae and Streptococcus pneumoniae have good evidence to support their use. [46] There is strong evidence for vaccinating children under the age of 2 against Streptococcus pneumoniae (pneumococcal conjugate vaccine). [73] [74] [75] Vaccinating children against Streptococcus pneumoniae has led to a decreased rate of these infections in adults, because many adults acquire infections from children. A Streptococcus pneumoniae vaccine is available for adults, and has been found to decrease the risk of invasive pneumococcal disease by 74%, but there is insufficient evidence to suggest using the pneumococcal vaccine to prevent pneumonia or death in the general adult population. [76] The CDC recommends that young children and adults over the age of 65 receive the pneumococcal vaccine, as well as older children or younger adults who have an increased risk of getting pneumococcal disease. [75] The pneumococcal vaccine has been shown to reduce the risk of community acquired pneumonia in people with chronic obstructive pulmonary disease (COPD), but does not reduce mortality or the risk of hospitalization for people with this condition. [77] People with COPD are suggested to have a pneumococcal vaccination. [77] Other vaccines for which there is support for a protective effect against pneumonia include pertussis, varicella, and measles. [78]


When influenza outbreaks occur, medications such as amantadine or rimantadine may help prevent the condition; however are associated with side effects. [79] Zanamivir or oseltamivir decrease the chance that people who are exposed to the virus will develop symptoms; however, it is recommended that potential side effects are taken into account. [80]


Smoking cessation [57] and reducing indoor air pollution, such as that from cooking indoors with wood or dung, are both recommended. [20] [22] Smoking appears to be the single biggest risk factor for pneumococcal pneumonia in otherwise-healthy adults. [65] Hand hygiene and coughing into one's sleeve may also be effective preventative measures. [78] Wearing surgical masks by the sick may also prevent illness. [65]

Appropriately treating underlying illnesses (such as HIV/AIDS, diabetes mellitus, and malnutrition) can decrease the risk of pneumonia. [22] [78] [81] In children less than 6 months of age, exclusive breast feeding reduces both the risk and severity of disease. [22] In those with HIV/AIDS and a CD4 count of less than 200 cells/uL the antibiotic trimethoprim/sulfamethoxazole decreases the risk of Pneumocystis pneumonia [82] and is also useful for prevention in those that are immunocomprised but do not have HIV. [83]

Testing pregnant women for Group B Streptococcus and Chlamydia trachomatis , and administering antibiotic treatment, if needed, reduces rates of pneumonia in infants; [84] [85] preventive measures for HIV transmission from mother to child may also be efficient. [86] Suctioning the mouth and throat of infants with meconium-stained amniotic fluid has not been found to reduce the rate of aspiration pneumonia and may cause potential harm, [87] thus this practice is not recommended in the majority of situations. [87] In the frail elderly good oral health care may lower the risk of aspiration pneumonia. [88] Zinc supplementation in children 2 months to five years old appears to reduce rates of pneumonia. [89]

For people with low levels of vitamin C in their diet or blood, taking vitamin C supplements may be suggested to decrease the risk of pneumonia, although there is no strong evidence of benefit. [90] There is insufficient evidence to recommend that the general population take vitamin C to prevent pneumonia. [90]

For adults and children in the hospital who require a respirator, there is no strong evidence indicating a difference between heat and moisture exchangers and heated humidifiers for preventing pneumonia. [91] There is no good evidence that one approach to mouth care is better than others in preventing nursing home acquired pneumonia. [92]


Urea>7 mmol/l1
Respiratory rate>301
SBP<90mmHg, DBP<60mmHg1

Antibiotics by mouth, rest, simple analgesics, and fluids usually suffice for complete resolution. [57] However, those with other medical conditions, the elderly, or those with significant trouble breathing may require more advanced care. If the symptoms worsen, the pneumonia does not improve with home treatment, or complications occur, hospitalization may be required. [57] Worldwide, approximately 7–13% of cases in children result in hospitalization, [20] whereas in the developed world between 22 and 42% of adults with community-acquired pneumonia are admitted. [57] The CURB-65 score is useful for determining the need for admission in adults. [57] If the score is 0 or 1, people can typically be managed at home; if it is 2, a short hospital stay or close follow-up is needed; if it is 3–5, hospitalization is recommended. [57] In children those with respiratory distress or oxygen saturations of less than 90% should be hospitalized. [93] The utility of chest physiotherapy in pneumonia has not yet been determined. [94] [ needs update ] [95] Non-invasive ventilation may be beneficial in those admitted to the intensive care unit. [96] Over-the-counter cough medicine has not been found to be effective, [97] nor has the use of zinc in children. [98] There is insufficient evidence for mucolytics. [97] There is no strong evidence to recommend that children who have non-measles related pneumonia take Vitamin A supplements. [99] For those with sepsis, 30 ml/kg of crystalloid should be infused to correct hypotension. [33] Vitamin D, as of 2018 is of unclear benefit in children. [100]


Antibiotics improve outcomes in those with bacterial pneumonia. [12] First dose of antibiotics should be given as soon as possible. [33] Increased use of antibiotics, however, may lead to the development of antimicrobial resistant strains of bacteria. [101] Antibiotic choice depends initially on the characteristics of the person affected, such as age, underlying health, and the location the infection was acquired. Antibiotic use is also associated with side effects such as nausea, diarrhea, dizziness, taste distortion, or headaches. [101] In the UK, treatment before culture results with amoxicillin is recommended as the first line for community-acquired pneumonia, with doxycycline or clarithromycin as alternatives. [57] In North America, where the "atypical" forms of community-acquired pneumonia are more common, macrolides (such as azithromycin or erythromycin), and doxycycline have displaced amoxicillin as first-line outpatient treatment in adults. [35] [102] In children with mild or moderate symptoms, amoxicillin taken by mouth remains the first line. [93] [103] [104] The use of fluoroquinolones in uncomplicated cases is discouraged due to concerns about side-effects and generating resistance in light of there being no greater clinical benefit. [35] [105]

For those who require hospitalization and caught their pneumonia in the community the use of a β-lactam such as cephazolin plus macrolide such as azithromycin or a fluoroquinolones is recommended. [106] Antibiotics by mouth and by injection appear to be similarly effective in children with severe pneumonia. [107]

The duration of treatment has traditionally been seven to ten days, but increasing evidence suggests that shorter courses (3–5 days) may be effective for certain types of pneumonia and may reduce the risk of antibiotic resistance. [108] [109] [110] [111] For pneumonia that is associated with a ventilator caused by non-fermenting Gram-negative bacilli (NF-GNB), a shorter course of antibiotics increases the risk of that pneumonia will return. [110] Recommendations for hospital-acquired pneumonia include third- and fourth-generation cephalosporins, carbapenems, fluoroquinolones, aminoglycosides, and vancomycin. [70] These antibiotics are often given intravenously and used in combination. [70] In those treated in hospital, more than 90% improve with the initial antibiotics. [25] For people with ventilator-acquired pneumonia, the choice of antibiotic therapy will depend on the person's risk of being infected with a strain of bacteria that is multi-drug resistant. [31] Once clinically stable, intravenous antibiotics should be swithced to oral antibiotics. [33] For those with Methicillin resistant Staphylococcus aureus (MRSA) or Legionella infections, prolonged antibiotics may be beneficial. [33]

The addition of corticosteroids to standard antibiotic treatment appears to improve outcomes, reducing death and morbidity for adults with severe community acquired pneumonia, and reducing death for adults and children with non-severe community acquired pneumonia. [112] [113] Side effects associated with the use of corticosteroids include high blood sugar. [112] They are therefore recommended in adults with severe community acquired pneumonia. [112] There is some evidence that adding corticosteroids to the standard PCP pneumonia treatment may be beneficial for people who are infected with HIV. [40]

The use of granulocyte colony stimulating factor (G-CSF) along with antibiotics does not appear to reduce mortality and routine use for treating pneumonia is not supported by evidence. [114]


Neuraminidase inhibitors may be used to treat viral pneumonia caused by influenza viruses (influenza A and influenza B). [11] No specific antiviral medications are recommended for other types of community acquired viral pneumonias including SARS coronavirus, adenovirus, hantavirus, and parainfluenza virus. [11] Influenza A may be treated with rimantadine or amantadine, while influenza A or B may be treated with oseltamivir, zanamivir or peramivir. [11] These are of most benefit if they are started within 48 hours of the onset of symptoms. [11] Many strains of H5N1 influenza A, also known as avian influenza or "bird flu", have shown resistance to rimantadine and amantadine. [11] The use of antibiotics in viral pneumonia is recommended by some experts, as it is impossible to rule out a complicating bacterial infection. [11] The British Thoracic Society recommends that antibiotics be withheld in those with mild disease. [11] The use of corticosteroids is controversial. [11]


In general, aspiration pneumonitis is treated conservatively with antibiotics indicated only for aspiration pneumonia. [115] The choice of antibiotic will depend on several factors, including the suspected causative organism and whether pneumonia was acquired in the community or developed in a hospital setting. Common options include clindamycin, a combination of a beta-lactam antibiotic and metronidazole, or an aminoglycoside. [116] Corticosteroids are sometimes used in aspiration pneumonia, but there is limited evidence to support their effectiveness. [115]


With treatment, most types of bacterial pneumonia will stabilize in 3–6 days. [3] It often takes a few weeks before most symptoms resolve. [3] X-ray finding typically clear within four weeks and mortality is low (less than 1%). [21] [117] In the elderly or people with other lung problems, recovery may take more than 12 weeks. In persons requiring hospitalization, mortality may be as high as 10%, and in those requiring intensive care it may reach 30–50%. [21] Pneumonia is the most common hospital-acquired infection that causes death. [25] Before the advent of antibiotics, mortality was typically 30% in those that were hospitalized. [18] However, for those whose lung condition deteriorates within 72 hours, the problem is usually due to sepsis. [33] If pneumonia deteriorates after 72 hours, it could be due to nosocomial infection or excerbation of other underlying co-morbidities. [33] About 10% of those discharged from hospital are readmitted due to underlying co-morbidities such as heart, lung, or neurology disorders, or due to new onset of pneumonia. [33]

Complications may occur in particular in the elderly and those with underlying health problems. [117] This may include, among others: empyema, lung abscess, bronchiolitis obliterans, acute respiratory distress syndrome, sepsis, and worsening of underlying health problems. [117]

Clinical prediction rules

Clinical prediction rules have been developed to more objectively predict outcomes of pneumonia. [25] These rules are often used in deciding whether or not to hospitalize the person. [25]

Pleural effusion, empyema, and abscess

A pleural effusion: as seen on chest X-ray. The A arrow indicates fluid layering in the right chest. The B arrow indicates the width of the right lung. The volume of the lung is reduced because of the collection of fluid around the lung. Pleural effusion.jpg
A pleural effusion: as seen on chest X-ray. The A arrow indicates fluid layering in the right chest. The B arrow indicates the width of the right lung. The volume of the lung is reduced because of the collection of fluid around the lung.

In pneumonia, a collection of fluid may form in the space that surrounds the lung. [119] Occasionally, microorganisms will infect this fluid, causing an empyema. [119] To distinguish an empyema from the more common simple parapneumonic effusion, the fluid may be collected with a needle (thoracentesis), and examined. [119] If this shows evidence of empyema, complete drainage of the fluid is necessary, often requiring a drainage catheter. [119] In severe cases of empyema, surgery may be needed. [119] If the infected fluid is not drained, the infection may persist, because antibiotics do not penetrate well into the pleural cavity. If the fluid is sterile, it must be drained only if it is causing symptoms or remains unresolved. [119]

In rare circumstances, bacteria in the lung will form a pocket of infected fluid called a lung abscess. [119] Lung abscesses can usually be seen with a chest X-ray but frequently require a chest CT scan to confirm the diagnosis. [119] Abscesses typically occur in aspiration pneumonia, and often contain several types of bacteria. Long-term antibiotics are usually adequate to treat a lung abscess, but sometimes the abscess must be drained by a surgeon or radiologist. [119]

Respiratory and circulatory failure

Pneumonia can cause respiratory failure by triggering acute respiratory distress syndrome (ARDS), which results from a combination of infection and inflammatory response. The lungs quickly fill with fluid and become stiff. This stiffness, combined with severe difficulties extracting oxygen due to the alveolar fluid, may require long periods of mechanical ventilation for survival. [36] Other causes of circulatory failure are hypoxemia, inflammation, and increased coagulability. [33]

Sepsis is a potential complication of pneumonia but occurs usually in people with poor immunity or hyposplenism. The organisms most commonly involved are Streptococcus pneumoniae, Haemophilus influenzae, and Klebsiella pneumoniae. Other causes of the symptoms should be considered such as a myocardial infarction or a pulmonary embolism. [120]


Deaths from lower respiratory infections per million persons in 2012
.mw-parser-output .refbegin{font-size:90%;margin-bottom:0.5em}.mw-parser-output .refbegin-hanging-indents>ul{list-style-type:none;margin-left:0}.mw-parser-output .refbegin-hanging-indents>ul>li,.mw-parser-output .refbegin-hanging-indents>dl>dd{margin-left:0;padding-left:3.2em;text-indent:-3.2em;list-style:none}.mw-parser-output .refbegin-100{font-size:100%}
1,210-2,085 Lower respiratory infections world map-Deaths per million persons-WHO2012.svg
Deaths from lower respiratory infections per million persons in 2012
Disability-adjusted life year for lower respiratory infections per 100,000 inhabitants in 2004
no data
less than 100
more than 7,000 Lower respiratory infections world map - DALY - WHO2004.svg
Disability-adjusted life year for lower respiratory infections per 100,000 inhabitants in 2004
  no data
  less than 100
  more than 7,000

Pneumonia is a common illness affecting approximately 450 million people a year and occurring in all parts of the world. [11] It is a major cause of death among all age groups resulting in 4 million deaths (7% of the world's total death) yearly. [11] [12] Rates are greatest in children less than five, and adults older than 75 years. [11] It occurs about five times more frequently in the developing world than in the developed world. [11] Viral pneumonia accounts for about 200 million cases. [11] In the United States, as of 2009, pneumonia is the 8th leading cause of death. [21]


In 2008, pneumonia occurred in approximately 156 million children (151 million in the developing world and 5 million in the developed world). [11] In 2010, it resulted in 1.3 million deaths, or 18% of all deaths in those under five years, of which 95% occurred in the developing world. [11] [20] [122] Countries with the greatest burden of disease include India (43 million), China (21 million) and Pakistan (10 million). [123] It is the leading cause of death among children in low income countries. [11] [12] Many of these deaths occur in the newborn period. The World Health Organization estimates that one in three newborn infant deaths is due to pneumonia. [124] Approximately half of these deaths can be prevented, as they are caused by the bacteria for which an effective vaccine is available. [125] In 2011, pneumonia was the most common reason for admission to the hospital after an emergency department visit in the U.S. for infants and children. [126]


WPA poster, 1936/1937 WPA Pneumonia Poster.jpg
WPA poster, 1936/1937

Pneumonia has been a common disease throughout human history. [127] The word is from Greek πνεύμων (pneúmōn) meaning "lung". [128] The symptoms were described by Hippocrates (c. 460–370 BC): [127] "Peripneumonia, and pleuritic affections, are to be thus observed: If the fever be acute, and if there be pains on either side, or in both, and if expiration be if cough be present, and the sputa expectorated be of a blond or livid color, or likewise thin, frothy, and florid, or having any other character different from the common... When pneumonia is at its height, the case is beyond remedy if he is not purged, and it is bad if he has dyspnoea, and urine that is thin and acrid, and if sweats come out about the neck and head, for such sweats are bad, as proceeding from the suffocation, rales, and the violence of the disease which is obtaining the upper hand." [129] However, Hippocrates referred to pneumonia as a disease "named by the ancients". He also reported the results of surgical drainage of empyemas. Maimonides (1135–1204 AD) observed: "The basic symptoms that occur in pneumonia and that are never lacking are as follows: acute fever, sticking pleuritic pain in the side, short rapid breaths, serrated pulse and cough." [130] This clinical description is quite similar to those found in modern textbooks, and it reflected the extent of medical knowledge through the Middle Ages into the 19th century.

Edwin Klebs was the first to observe bacteria in the airways of persons having died of pneumonia in 1875. [131] Initial work identifying the two common bacterial causes, Streptococcus pneumoniae and Klebsiella pneumoniae, was performed by Carl Friedländer [132] and Albert Fraenkel [133] in 1882 and 1884, respectively. Friedländer's initial work introduced the Gram stain, a fundamental laboratory test still used today to identify and categorize bacteria. Christian Gram's paper describing the procedure in 1884 helped to differentiate the two bacteria, and showed that pneumonia could be caused by more than one microorganism. [134]

Sir William Osler, known as "the father of modern medicine", appreciated the death and disability caused by pneumonia, describing it as the "captain of the men of death" in 1918, as it had overtaken tuberculosis as one of the leading causes of death in this time. This phrase was originally coined by John Bunyan in reference to "consumption" (tuberculosis). [135] [136] Osler also described pneumonia as "the old man's friend" as death was often quick and painless when there were much slower and more painful ways to die. [18]

Several developments in the 1900s improved the outcome for those with pneumonia. With the advent of penicillin and other antibiotics, modern surgical techniques, and intensive care in the 20th century, mortality from pneumonia, which had approached 30%, dropped precipitously in the developed world. Vaccination of infants against Haemophilus influenzae type B began in 1988 and led to a dramatic decline in cases shortly thereafter. [137] Vaccination against Streptococcus pneumoniae in adults began in 1977, and in children in 2000, resulting in a similar decline. [138]

Society and culture


Due to the relatively low awareness of the disease, 12 November was declared as the annual World Pneumonia Day, a day for concerned citizens and policy makers to take action against the disease, in 2009. [139] [140]


The global economic cost of community-acquired pneumonia has been estimated at $17 billion annually. [21] Other estimates are considerably higher. In 2012 the estimated aggregate costs of treating pneumonia in the United States were $20 billion; [141] the median cost of a single pneumonia-related hospitalization is over $15,000. [142] According to data released by the Centers for Medicare and Medicaid Services, average 2012 hospital charges for inpatient treatment of uncomplicated pneumonia in the U.S. were $24,549 and ranged as high as $124,000. The average cost of an emergency room consult for pneumonia was $943 and the average cost for medication was $66. [143] Aggregate annual costs of treating pneumonia in Europe have been estimated at €10 billion. [144]

Related Research Articles

Common cold common viral infection of upper respiratory tract

The common cold, also known simply as a cold, is a viral infectious disease of the upper respiratory tract that primarily affects the nose. The throat, sinuses, and larynx may also be affected. Signs and symptoms may appear less than two days after exposure to the virus. These may include coughing, sore throat, runny nose, sneezing, headache, and fever. People usually recover in seven to ten days, but some symptoms may last up to three weeks. Occasionally those with other health problems may develop pneumonia.

Otitis media otitis which involves inflammation of the middle ear

Otitis media is a group of inflammatory diseases of the middle ear. The two main types are acute otitis media (AOM) and otitis media with effusion (OME). AOM is an infection of rapid onset that usually presents with ear pain. In young children this may result in pulling at the ear, increased crying, and poor sleep. Decreased eating and a fever may also be present. OME is typically not associated with symptoms. Occasionally a feeling of fullness is described. It is defined as the presence of non-infectious fluid in the middle ear for more than three months. Chronic suppurative otitis media (CSOM) is middle ear inflammation of greater than two weeks that results in episodes of discharge from the ear. It may be a complication of acute otitis media. Pain is rarely present. All three may be associated with hearing loss. The hearing loss in OME, due to its chronic nature, may affect a child's ability to learn.

Pharyngitis type of upper respiratory tract infection

Pharyngitis is inflammation of the back of the throat, known as the pharynx. It typically results in a sore throat and fever. Other symptoms may include a runny nose, cough, headache, and a hoarse voice. Symptoms usually last three to five days. Complications can include sinusitis and acute otitis media. Pharyngitis is a type of upper respiratory tract infection.

Cold medicine Agents whose purpose is to suppress coughing

Cold medicines are medications used by people with the common cold, cough, or related conditions. There is, however, no good evidence that cough medications reduce coughing. While they are used by 10% of American children in any given week, they are not recommended in Canada and the United States in children 6 years or younger because of lack of evidence showing effect and concerns of harm.

Acute bronchitis short-term inflammation of the bronchi (large and medium-sized airways) of the lungs

Acute bronchitis, also known as a chest cold, is short-term inflammation of the bronchi of the lungs. The most common symptom is a cough. Other symptoms include coughing up mucus, wheezing, shortness of breath, fever, and chest discomfort. The infection may last from a few to ten days. The cough may persist for several weeks afterward with the total duration of symptoms usually around three weeks. Some have symptoms for up to six weeks.

Croup respiratory condition that is usually triggered by an acute viral infection of the upper airway

Croup, also known as laryngotracheobronchitis, is a type of respiratory infection that is usually caused by a virus. The infection leads to swelling inside the trachea, which interferes with normal breathing and produces the classic symptoms of "barking" cough, stridor, and a hoarse voice. Fever and runny nose may also be present. These symptoms may be mild, moderate, or severe. Often it starts or is worse at night. It normally lasts one to two days.

Bronchiectasis congenital disorder of respiratory system

Bronchiectasis is a disease in which there is permanent enlargement of parts of the airways of the lung. Symptoms typically include a chronic cough with mucus production. Other symptoms include shortness of breath, coughing up blood, and chest pain. Wheezing and nail clubbing may also occur. Those with the disease often get frequent lung infections.

Atypical pneumonia, also known as walking pneumonia, is the type of pneumonia not caused by one of the pathogens most commonly associated with the disease. Its clinical presentation contrasts to that of "typical" pneumonia. A variety of microorganisms can cause it. When it develops independently from another disease it is called primary atypical pneumonia (PAP).

Upper respiratory tract infection

Upper respiratory tract infections (URTI) are illnesses caused by an acute infection which involves the upper respiratory tract including the nose, sinuses, pharynx or larynx. This commonly includes nasal obstruction, sore throat, tonsillitis, pharyngitis, laryngitis, sinusitis, otitis media, and the common cold. Most infections are viral in nature and in other instances the cause is bacterial. Upper respiratory tract infections can also be fungal or helminth in origin, but these are far less common.

Pleural empyema empyema (an accumulation of pus) in the pleural cavity that can develop when bacteria invade the pleural space, usually in the context of a pneumonia

Pleural empyema is a collection of pus in the pleural cavity caused by microorganisms, usually bacteria. Often it happens in the context of a pneumonia, injury, or chest surgery. It is one of the various kinds of pleural effusion. There are three stages: exudative, when there is an increase in pleural fluid with or without the presence of pus; fibrinopurulent, when fibrous septa form localized pus pockets; and the final organizing stage, when there is scarring of the pleura membranes with possible inability of the lung to expand. Simple pleural effusions occur in up to 40% of bacterial pneumonias. They are usually small and resolve with appropriate antibiotic therapy. If however an empyema develops additional intervention is required.

<i>Haemophilus influenzae</i> species of bacterium

Haemophilus influenzae is a Gram-negative, coccobacillary, facultatively anaerobic pathogenic bacterium belonging to the Pasteurellaceae family. H. influenzae was first described in 1892 by Richard Pfeiffer during an influenza pandemic.

Lower respiratory tract infection

Lower respiratory tract infection (LRTI), while often used as a synonym for pneumonia, can also be applied to other types of infection including lung abscess and acute bronchitis. Symptoms include shortness of breath, weakness, fever, coughing and fatigue.

Bacterial pneumonia is a type of pneumonia caused by bacterial infection.

Interstitial lung disease group of lung diseases affecting the interstitium (the tissue and space around the air sacs of the lungs)

Interstitial lung disease (ILD), or diffuse parenchymal lung disease (DPLD), is a group of lung diseases affecting the interstitium. It concerns alveolar epithelium, pulmonary capillary endothelium, basement membrane, and perivascular and perilymphatic tissues. It may occur when an injury to the lungs triggers an abnormal healing response. Ordinarily, the body generates just the right amount of tissue to repair damage, but in interstitial lung disease, the repair process goes awry and the tissue around the air sacs (alveoli) becomes scarred and thickened. This makes it more difficult for oxygen to pass into the bloodstream. The term ILD is used to distinguish these diseases from obstructive airways diseases.

Community-acquired pneumonia refers to pneumonia contracted by a person with little contact with the healthcare system. The chief difference between hospital-acquired pneumonia (HAP) and CAP is that patients with HAP live in long-term care facilities or have recently visited a hospital. CAP is common, affecting people of all ages, and its symptoms occur as a result of oxygen-absorbing areas of the lung (alveoli) filling with fluid. This inhibits lung function, causing dyspnea, fever, chest pains and cough.

Respiratory tract infection any number of infectious diseases involving the respiratory tract

Respiratory tract infection (RTI) refers to any of a number of infectious diseases involving the respiratory tract. An infection of this type is normally further classified as an upper respiratory tract infection or a lower respiratory tract infection. Lower respiratory infections, such as pneumonia, tend to be far more serious conditions than upper respiratory infections, such as the common cold.

Bronchitis type of lower respiratory disease

Bronchitis is an inflammation of the bronchi in the lungs. Symptoms include coughing up mucus, wheezing, shortness of breath, and chest discomfort. Bronchitis is divided into two types: acute and chronic. Acute bronchitis is also known as a chest cold.

The acute chest syndrome is a vaso-occlusive crisis of the pulmonary vasculature commonly seen in people with sickle cell anemia. This condition commonly manifests with a new opacification of the lung(s) on a chest x-ray.

A pneumococcal infection is an infection caused by the bacterium Streptococcus pneumoniae, which is also called the pneumococcus. S. pneumoniae is a common member of the bacterial flora colonizing the nose and throat of 5–10% of healthy adults and 20–40% of healthy children. However, it is also a cause of significant disease, being a leading cause of pneumonia, bacterial meningitis, and sepsis. The World Health Organization estimate that in 2005 pneumococcal infections were responsible for the death of 1.6 million children worldwide.

Acute exacerbation of chronic obstructive pulmonary disease

Acute exacerbation of COPD is a sudden worsening of COPD symptoms that typically lasts for several days. It may be triggered by an infection with bacteria or viruses or by environmental pollutants. Typically, infections cause 75% or more of the exacerbations; bacteria can roughly be found in 25% of cases, viruses in another 25%, and both viruses and bacteria in another 25%. Airway inflammation is increased during the exacerbation resulting in increased hyperinflation, reduced expiratory air flow and decreased gas exchange.


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