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In epidemiology, incidence reflects the number of new cases of a given medical condition in a population within a specified period of time.
| | This article needs additional citations for verification .(November 2007) |
In epidemiology, incidence reflects the number of new cases of a given medical condition in a population within a specified period of time.
Incidence proportion (IP), also known as cumulative incidence, is defined as the probability that a particular event, such as occurrence of a particular disease, has occurred in a specified period: [1]
For example, if a population contains 1,000 persons and 28 develop a condition from the time the disease first occurred until two years later, the cumulative incidence is 28 cases per 1,000 persons, i.e. 2.8%.
The incidence rate can be calculated by dividing the number of subjects developing a disease by the total time at risk from all patients: [1]
One of the important advantages of incidence rate is that it doesn't require all subjects to be present for the whole study because it's only interested in the time at risk. [1]
Incidence should not be confused with prevalence, which is the proportion of cases in the population at a given time rather than rate of occurrence of new cases. Thus, incidence conveys information about the risk of contracting the disease, whereas prevalence indicates how widespread the disease is. Prevalence is the proportion of the total number of cases to the total population and is more a measure of the burden of the disease on society with no regard to time at risk or when subjects may have been exposed to a possible risk factor. Prevalence can also be measured with respect to a specific subgroup of a population. Incidence is usually more useful than prevalence in understanding the disease etiology: for example, if the incidence rate of a disease in a population increases, then there is a risk factor that promotes the incidence.
For example, consider a disease that takes a long time to cure and was widespread in 2002 but dissipated in 2003. This disease will have both high incidence and high prevalence in 2002, but in 2003 it will have a low incidence yet will continue to have a high prevalence (because it takes a long time to cure, so the fraction of individuals that are affected remains high). In contrast, a disease that has a short duration may have a low prevalence and a high incidence. When the incidence is approximately constant for the duration of the disease, prevalence is approximately the product of disease incidence and average disease duration, so prevalence = incidence × duration. The importance of this equation is in the relation between prevalence and incidence; for example, when the incidence increases, then the prevalence must also increase. Note that this relation does not hold for age-specific prevalence and incidence, where the relation becomes more complicated. [2]
Consider the following example. Say you are looking at a sample population of 225 people, and want to determine the incidence rate of developing HIV over a 10-year period:
If you were to measure prevalence you would simply take the total number of cases (25 + 20 + 30 = 75) and divide by your sample population (225). So prevalence would be 75/225 = 0.33 or 33% (by the end of the study). This tells you how widespread HIV is in your sample population, but little about the actual risk of developing HIV for any person over a coming year.
To measure incidence rate you must take into account how many years each person contributed to the study, and when they developed HIV because when a subject develops HIV he stops being at risk. When it is not known exactly when a person develops the disease in question, epidemiologists frequently use the actuarial method, and assume it was developed at a half-way point between follow-ups.[ citation needed ] In this calculation:
That is a total of (1500 + 275) = 1775 person-years of life. Now take the 50 new cases of HIV, and divide by 1775 to get 0.028, or 28 cases of HIV per 1000 population, per year. In other words, if you were to follow 1000 people for one year, you would see 28 new cases of HIV. This is a much more accurate measure of risk than prevalence.
Tuberculosis (TB), also known colloquially as the "white death", or historically as consumption, is an infectious disease usually caused by Mycobacterium tuberculosis (MTB) bacteria. Tuberculosis generally affects the lungs, but it can also affect other parts of the body. Most infections show no symptoms, in which case it is known as latent tuberculosis. Around 10% of latent infections progress to active disease which, if left untreated, kill about half of those affected. Typical symptoms of active TB are chronic cough with blood-containing mucus, fever, night sweats, and weight loss. Infection of other organs can cause a wide range of symptoms.
Non-Hodgkin lymphoma (NHL), also known as non-Hodgkin's lymphoma, is a group of blood cancers that includes all types of lymphomas except Hodgkin lymphomas. Symptoms include enlarged lymph nodes, fever, night sweats, weight loss, and tiredness. Other symptoms may include bone pain, chest pain, or itchiness. Some forms are slow-growing while others are fast-growing. Unlike Hodgkin lymphoma, which spreads contiguously, NHL is largely a systemic illness.
In epidemiology, prevalence is the proportion of a particular population found to be affected by a medical condition at a specific time. It is derived by comparing the number of people found to have the condition with the total number of people studied and is usually expressed as a fraction, a percentage, or the number of cases per 10,000 or 100,000 people. Prevalence is most often used in questionnaire studies.
The spread of HIV/AIDS has affected millions of people worldwide; AIDS is considered a pandemic. The World Health Organization (WHO) estimated that in 2016 there were 36.7 million people worldwide living with HIV/AIDS, with 1.8 million new HIV infections per year and 1 million deaths due to AIDS. Misconceptions about HIV and AIDS arise from several different sources, from simple ignorance and misunderstandings about scientific knowledge regarding HIV infections and the cause of AIDS to misinformation propagated by individuals and groups with ideological stances that deny a causative relationship between HIV infection and the development of AIDS. Below is a list and explanations of some common misconceptions and their rebuttals.
Human T-cell lymphotropic virus type 1 or human T-lymphotropic virus (HTLV-I), also called the adult T-cell lymphoma virus type 1, is a retrovirus of the human T-lymphotropic virus (HTLV) family.
Men who have sex with men (MSM) are men who engage in sexual activity with other men, regardless of their sexual orientation or sexual identity. The term was created by epidemiologists in the 1990s, to better study and communicate the spread of sexually transmitted infections such as HIV/AIDS between all sexually active males, not strictly those identifying as gay, bisexual, pansexual or various other sexualities, but also for example male prostitutes. The term is often used in medical literature and social research to describe such men as a group. It does not describe any specific kind of sexual activity, and which activities are covered by the term depends on context. The alternative term "males who have sex with males" is sometimes considered more accurate in cases where those described may not be legal adults.
Compartmental models are a very general modelling technique. They are often applied to the mathematical modelling of infectious diseases. The population is assigned to compartments with labels – for example, S, I, or R,. People may progress between compartments. The order of the labels usually shows the flow patterns between the compartments; for example SEIS means susceptible, exposed, infectious, then susceptible again.
The global pandemic of HIV/AIDS began in 1981, and is an ongoing worldwide public health issue. According to the World Health Organization (WHO), by 2023, HIV/AIDS had killed approximately 40.4 million people, and approximately 39 million people were infected with HIV globally. Of these, 29.8 million people (75%) are receiving antiretroviral treatment. There were about 630,000 deaths from HIV/AIDS in 2022. The 2015 Global Burden of Disease Study estimated that the global incidence of HIV infection peaked in 1997 at 3.3 million per year. Global incidence fell rapidly from 1997 to 2005, to about 2.6 million per year. Incidence of HIV has continued to fall, decreasing by 23% from 2010 to 2020, with progress dominated by decreases in Eastern Africa and Southern Africa. As of 2023, there are about 1.3 million new infections of HIV per year globally.
Collagenous colitis is an inflammatory condition of the colon. Together with the related condition lymphocytic colitis, it is a subtype of microscopic colitis, which is characterized by inflammation that specifically affects the colon, and a clinical presentation that involves watery diarrhea but a lack of rectal bleeding. Microscopic colitis does not usually cause macroscopic changes to the colon that allow a visual diagnosis during colonoscopy, instead causing microscopic changes that can be detected through histopathological examination of colonic biopsies. The nature of these microscopic changes is what differentiates collagenous from lymphocytic colitis, with the characteristic finding in collagenous colitis being depositions of collagen in the connective tissue between the colonic glands. Collagenous colitis, and microscopic colitis as a whole, is sometimes considered to be an inflammatory bowel disease (IBD) along with Crohn's disease and ulcerative colitis. However, little is known about the etiology of microscopic colitis, and so the degree of similarity to the inflammatory bowel diseases is uncertain.
The epidemiology of autism is the study of the incidence and distribution of autism spectrum disorders (ASD). A 2022 systematic review of global prevalence of autism spectrum disorders found a median prevalence of 1% in children in studies published from 2012 to 2021, with a trend of increasing prevalence over time. However, the study's 1% figure may reflect an underestimate of prevalence in low- and middle-income countries.
In Western Europe, the routes of transmission of HIV are diverse, including paid sex, sex between men, intravenous drugs, mother to child transmission, and heterosexual sex. However, many new infections in this region occur through contact with HIV-infected individuals from other regions. In some areas of Europe, such as the Baltic countries, the most common route of HIV transmission is through injecting drug use and heterosexual sex, including paid sex.
A subclinical infection—sometimes called a preinfection or inapparent infection—is an infection by a pathogen that causes few or no signs or symptoms of infection in the host. Subclinical infections can occur in both humans and animals. Depending on the pathogen, which can be a virus or intestinal parasite, the host may be infectious and able to transmit the pathogen without ever developing symptoms; such a host is called an asymptomatic carrier. Many pathogens, including HIV, typhoid fever, and coronaviruses such as COVID-19 spread in their host populations through subclinical infection.
HIV superinfection is a condition in which a person with an established human immunodeficiency virus infection acquires a second strain of HIV, often of a different subtype. These can form a recombinant strain that co-exists with the strain from the initial infection, as well from reinfection with a new virus strain, and may cause more rapid disease progression or carry multiple resistances to certain HIV medications.
Multidrug-resistant tuberculosis (MDR-TB) is a form of tuberculosis (TB) infection caused by bacteria that are resistant to treatment with at least two of the most powerful first-line anti-TB medications (drugs): isoniazid and rifampicin. Some forms of TB are also resistant to second-line medications, and are called extensively drug-resistant TB (XDR-TB).
The situation with the spread of HIV/AIDS in Russia is described by some researchers as an epidemic. The first cases of human immunodeficiency virus infection were recorded in the USSR in 1985-1987. Patient zero is officially considered to be a military interpreter who worked in Tanzania in the early 1980s and was infected by a local man during sexual contact. After 1988—1989 Elista HIV outbreak, the disease became known to the general public and the first AIDS centers were established. In 1995-1996, the virus spread among injecting drug users (IDUs) and soon expanded throughout the country. By 2006, HIV had spread beyond the vulnerable IDU group, endangering their heterosexual partners and potentially the entire population.
The Philippines has one of the lowest rates of infection of HIV/AIDS, yet has one of the fastest growing number of cases worldwide. The Philippines is one of seven countries with growth in number of cases of over 25%, from 2001 to 2009.
The Dominican Republic has a 0.7 percent prevalence rate of HIV/AIDS, among the lowest percentage-wise in the Caribbean region. However, it has the second most cases in the Caribbean region in total web|url=http://www.avert.org/caribbean-hiv-aids-statistics.htm |title=Caribbean HIV & AIDS Statistics|date=21 July 2015}}</ref> with an estimated 46,000 HIV/AIDS-positive Dominicans as of 2013.
Epidemiology of periodontal disease is the study of patterns, causes, and effects of periodontal diseases. Periodontal disease is a disease affecting the tissue surrounding the teeth. This causes the gums and the teeth to separate making spaces that become infected. The immune system tries to fight the toxins breaking down the bone and tissue connecting to the teeth to the gums. The teeth will have to be removed. This is an advance stage of gum disease that has multiple definitions. Adult periodontitis affects less than 10 to 15% of the population in industrialized countries, mainly adults around the ages of 50 to 60. The disease is now declining world-wide.
Pneumonia is a common respiratory infection, affecting approximately 450 million people a year and occurring in all parts of the world. It is a major cause of death among all age groups, resulting in 1.4 million deaths in 2010 and 3.0 million deaths in 2016.
The co-epidemic of tuberculosis (TB) and human immunodeficiency virus (HIV) is one of the major global health challenges in the present time. The World Health Organization (WHO) reports 9.2 million new cases of TB in 2006 of whom 7.7% were HIV-infected. Tuberculosis is the most common contagious infection in HIV-Immunocompromised patients leading to death. These diseases act in combination as HIV drives a decline in immunity while tuberculosis progresses due to defective immune status. This condition becomes more severe in case of multi-drug (MDRTB) and extensively drug resistant TB (XDRTB), which are difficult to treat and contribute to increased mortality. Tuberculosis can occur at any stage of HIV infection. The risk and severity of tuberculosis increases soon after infection with HIV. A study on gold miners of South Africa revealed that the risk of TB was doubled during the first year after HIV seroconversion. Although tuberculosis can be a relatively early manifestation of HIV infection, it is important to note that the risk of tuberculosis progresses as the CD4 cell count decreases along with the progression of HIV infection. The risk of TB generally remains high in HIV-infected patients, remaining above the background risk of the general population even with effective immune reconstitution and high CD4 cell counts with antiretroviral therapy.
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