Contagious disease

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A contagious disease is a disease that readily spread (that is, communicated) by transmission of a pathogen from an infected person to another person. [1] Contagious diseases vary in how readily they are communicated. For example, COVID-19, which spreads by transmission of the SARS-CoV-2 coronavirus from one person to another, is extremely contagious. [2]


Conversely, a non-contagious disease either cannot be transmitted from one person to another or the probability of transmitting the disease to another person is low. [3]

A disease is often known to be contagious before medical science discovers its causative agent. Koch's postulates, which were published at the end of the 19th century, were the standard for the next 100 years or more, especially with diseases caused by bacteria. Microbial pathogenesis attempts to account for diseases caused by a virus.

Historical meaning

Originally, the term referred to a contagion (a derivative of 'contact') or disease transmissible only by direct physical contact. In the modern-day, the term has sometimes been broadened to encompass any communicable or infectious disease. Often the word can only be understood in context, where it is used to emphasise very infectious, easily transmitted, or especially severe communicable disease.

In 1849, John Snow first proposed that cholera was a contagious disease.

Effect on public health response

This clinic uses negative room pressure to prevent disease transmission NIH Clinical Center - Special Clinical Studies Unit.jpg
This clinic uses negative room pressure to prevent disease transmission

Most epidemics are caused by contagious diseases, with occasional exceptions, such as yellow fever. The spread of non-contagious communicable diseases is changed either very little or not at all by medical isolation of ill persons or medical quarantine for exposed persons. Thus, a "contagious disease" is sometimes defined in practical terms, as a disease for which isolation or quarantine are useful public health responses. [4] [ failed verification ]

Some locations are better suited for the research into the contagious pathogens due to the reduced risk of transmission afforded by a remote or isolated location.

Negative room pressure is a technique in health care facilities based on aerobiological designs.

See also

Related Research Articles

Disease Abnormal condition that negatively affects an organism

A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not due to any immediate external injury. Diseases are often known to be medical conditions that are associated with specific signs and symptoms. A disease may be caused by external factors such as pathogens or by internal dysfunctions. For example, internal dysfunctions of the immune system can produce a variety of different diseases, including various forms of immunodeficiency, hypersensitivity, allergies and autoimmune disorders.

Quarantine Epidemiological intervention to prevent disease transmission

A quarantine is a restriction on the movement of people, animals and goods which is intended to prevent the spread of disease or pests. It is often used in connection to disease and illness, preventing the movement of those who may have been exposed to a communicable disease, yet do not have a confirmed medical diagnosis. It is distinct from medical isolation, in which those confirmed to be infected with a communicable disease are isolated from the healthy population. Quarantine considerations are often one aspect of border control.

Infection Invasion of an organisms body tissues by disease-causing agents

An infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host tissues to the infectious agents and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable disease, is an illness resulting from an infection.

Epidemic Debilitating or deadly disease

An epidemic is the rapid spread of disease to a large number of people in a given population within a short period of time. For example, in meningococcal infections, an attack rate in excess of 15 cases per 100,000 people for two consecutive weeks is considered an epidemic.

Asymptomatic carrier Organism which has become infected with a pathogen but displays no symptoms

An asymptomatic carrier is a person or other organism that has become infected with a pathogen, but that displays no signs or symptoms.

In medicine, public health, and biology, transmission is the passing of a pathogen causing communicable disease from an infected host individual or group to a particular individual or group, regardless of whether the other individual was previously infected.The term strictly refers to the transmission of microorganisms directly from one individual to another by one or more of the following means:

Natural reservoir Living host, such as an animal or a plant, inside of which an infectious pathogen naturally lives and reproduces

In infectious disease ecology and epidemiology, a natural reservoir, also known as a disease reservoir or a reservoir of infection, is the population of organisms or the specific environment in which an infectious pathogen naturally lives and reproduces, or upon which the pathogen primarily depends for its survival. A reservoir is usually a living host of a certain species, such as an animal or a plant, inside of which a pathogen survives, often without causing disease for the reservoir itself. By some definitions a reservoir may also be an environment external to an organism, such as a volume of contaminated air or water.

Contact tracing Finding and identifying people in contact with someone with an infectious disease

In public health, contact tracing is the process of identifying persons who may have come into contact with an infected person ("contacts") and subsequent collection of further information about these contacts. By tracing the contacts of infected individuals, testing them for infection, isolating or treating the infected, and tracing their contacts, public health aims to reduce infections in the population. Diseases for which contact tracing is commonly performed include tuberculosis, vaccine-preventable infections like measles, sexually transmitted infections, blood-borne infections, Ebola, some serious bacterial infections, and novel virus infections. The goals of contact tracing are:

National Centre for Infectious Diseases Specialised hospital in Singapore

The National Centre for Infectious Diseases, previously known as the Communicable Disease Centre, is a national public health institute under the Ministry of Health of Singapore. It is located next to Tan Tock Seng Hospital in Novena.

A transfusion transmitted infection (TTI) is a virus, parasite, or other potential pathogen that can be transmitted in donated blood through a transfusion to a recipient. The term is usually limited to known pathogens, but also sometimes includes agents such as Simian foamy virus which are not known to cause disease.

Isolation (health care) Measure taken to prevent contagious diseases from being spread

In health care facilities, isolation represents one of several measures that can be taken to implement in infection control: the prevention of communicable diseases from being transmitted from a patient to other patients, health care workers, and visitors, or from outsiders to a particular patient. Various forms of isolation exist, in some of which contact procedures are modified, and others in which the patient is kept away from all other people. In a system devised, and periodically revised, by the U.S. Centers for Disease Control and Prevention (CDC), various levels of patient isolation comprise application of one or more formally described "precaution".

Skin infections and wrestling is the role of skin infections in wrestling. This is an important topic in wrestling since breaks in the skin are easily invaded by bacteria or fungi and wrestling involves constant physical contact that can cause transmission of viral, bacterial, and fungal pathogens. These infections can also be spread through indirect contact, for example, from the skin flora of an infected individual to a wrestling mat, to another wrestler. According to the National Collegiate Athletic Association's (NCAA) Injury Surveillance System, ten percent of all time-loss injuries in wrestling are due to skin infections.

Airborne transmission Disease transmission by airborne particles

An airborne transmission is disease transmission through small particulates that can be transmitted through the air over time and distance. Diseases capable of airborne transmission include many of considerable importance both in human and veterinary medicine. The relevant pathogens may be viruses, bacteria, or fungi, and they may be spread through breathing, talking, coughing, sneezing, raising of dust, spraying of liquids, flushing toilets, or any activities which generate aerosol particles or droplets. Human airborne diseases do not include conditions caused by air pollution such as volatile organic compounds (VOCs), gases and any airborne particles.

A fomite or fomes is any inanimate object that, when contaminated with or exposed to infectious agents, can transfer disease to a new host. In the 21st century, the role of fomites in disease transfer is higher than ever in human history because of the indoor lifestyle.

Superspreading event event in which an infectious disease is spread much more than usual

A superspreading event (SSEV) is an event in which an infectious disease is spread much more than usual, while an unusually contagious organism infected with a disease is known as a superspreader. In the context of a human-borne illness, a superspreader is an individual who is more likely to infect others, compared with a typical infected person. Such superspreaders are of particular concern in epidemiology.

The Division of Global Migration and Quarantine (DGMQ) is the part of the U.S. government responsible for U.S. Quarantine Stations and issuing quarantine orders. It is part of the National Center for Emerging and Zoonotic Infectious Diseases within the Centers for Disease Control and Prevention (CDC).

In epidemiology, a non-pharmaceutical intervention (NPI) is any method to reduce the spread of an epidemic disease without requiring pharmaceutical drug treatments. The US Centers for Disease Control and Prevention (CDC) points to Personal NPIs, Community NPIs and Environmental NPIs. NPI have been recommended for pandemic influenza at both local and global levels, and studied at large scale during the 2009 swine flu pandemic and the COVID-19 pandemic. NPIs are a set of measures that can be utilized at any time, and are used in the period between the emergence of an epidemic disease, and the deployment of an effective vaccine.

In epidemiology, particularly in the discussion of infectious disease dynamics (modeling), the latent period is the time interval between when an individual or host is infected by a pathogen and when he or she becomes infectious, i.e. capable of transmitting pathogens to other susceptible individuals.

Infectious period

In epidemiology, particularly in the discussion of infectious disease dynamics, the infectious period is the time interval during which a host is infectious, i.e. capable of directly or indirectly transmitting pathogenic infectious agents or pathogens to another susceptible host. The infectious period can start before, during or after the onset of symptoms, and it may stop before or after the symptoms stop showing. It is also known in the literature by a variety of synonymous terms such as the infective period, the period of infectiousness, communicability period, the period of communicability, contagious period, the period of contagiousness, transmission period or transmissibility period. The degree of infectiousness is not constant but varies through the infectious period.

Transmission of COVID-19 Mechanisms that spread coronavirus disease 2019

The transmission of COVID-19 is the passing of coronavirus disease 2019 from person to person. The disease is mainly transmitted via the respiratory route when people inhale droplets and particles that infected people release as they breathe, talk, cough, sneeze, or sing. Infected people are more likely to transmit COVID-19 when they are physically close to others. However, infection can occur over longer distances, particularly indoors.


  1. "Merriam-Webster dictionary definition of contagious disease" . Retrieved 2009-11-27.
  2. "SARS-CoV-2, SARS-CoV, and MERS-CoV viral load dynamics, duration of viral shedding, and infectiousness: a systematic review and meta-analysis". The Lancet Microbe. 2 (1): e13–e22. 2021-01-01. doi:10.1016/S2666-5247(20)30172-5. hdl: 10023/21023 . ISSN   2666-5247.
  3. Non-Contagious Diseases - Contact With, accessed 27 January 2020.
  4. A primer from the CDC on quarantine and its uses against contagious disease spread Accessed Nov. 27, 2009.