A Guide to HIV/AIDS Epidemiological and Surveillance Terms

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Frequently Used Terms in HIV/AIDS Monitoring and Epidemiological Research in Canada

E

ENDEMIC
(See also EPIDEMIC)

The standard epidemiological definition of the term endemic is the constant presence of a disease in a given geographic area or within a given population. It may also refer to a disease that is usually present at a relatively high prevalence and incidence rate in comparison with other areas or populations.

In the area of HIV/AIDS research, there is another definition of the term endemic that may be used. It may be used to refer to a country where the predominant way people become infected with HIV is through heterosexual contact. An "endemic" country is also commonly referred to as a Pattern II country.

In Canadian HIV/AIDS surveillance reporting, there is an exposure category that can be assigned to a person infected with HIV whose highest risk of HIV transmission was being born in an endemic country.

EPIDEMIC
(See also EPIDEMIOLOGY)

An epidemic is the occurrence of a greater number of cases of a disease than would normally be expected to occur in a population, community or region.

The AIDS epidemic was first identified soon after the first cases were diagnosed in the early 1980s. By the late 1980s, HIV/AIDS was affecting the entire world, an epidemic to which the word "pandemic" is applied.

EPIDEMIOLOGY
(See also FAQ 23)

Epidemiology refers to the study of the occurrence, distribution and determining factors associated with health events and diseases in a population.

The aims of epidemiology are to discover the sources and causes of health events and disease occurrences and to find ways to control and prevent them.

For example, the Polaris Study currently under way across Ontario is an example of an epidemiological study. The objectives of the study include determining the rates of new HIV infections, identifying factors associated with HIV infection, and evaluating the impact of early treatment and care on outcomes.

ETHNIC CATEGORY
(See also ETHNICITY REPORTING)

In reporting AIDS cases and positive HIV test reports in Canada, the person receiving the diagnosis and/or the health care provider may record one of seven choices describing the person's ethnic status.

An ethnic group is a group of people who share a distinctive cultural and historical tradition, and is often associated with race or nationality.

The choices of ethnic categories are as follows:

• Aboriginal
  This category includes, for example, Inuit, Métis, Native Indian and "Aboriginal Unspecified" people.

• Asian
  This category includes, for example, people from Cambodia, China, Indonesia, Japan, Laos, Korea, the Philippines and Viet Nam.

• Black
  This category includes, for example, people from Zimbabwe, Angola, Haiti and Jamaica.

• Latin American
  This category includes, for example, people from Central America, Mexico and South America.

• South Asian/West Asian/Arab
  This category includes, for example, people from Armenia, Bangladesh, Egypt, Iran, Lebanon, Morocco, Pakistan and Sri Lanka.

• White
  This category includes people who identify themselves as White or whose health care provider identifies them as White.

• Other
  If none of the above choices describes the individual's status, "Other" is marked off on the form.

ETHNICITY REPORTING
(See also FAQs 8, 14)

Ethnicity reporting is recording the ethnic group of the individual with a diagnosis of HIV infection or AIDS. Ethnicity may be either self-reported by the person being tested or may be identified by the health care provider. Documentation of ethnicity for reported AIDS cases and positive HIV test reports is helpful in driving the development and evaluation of prevention and treatment programs.

In considering information about reported AIDS cases or positive HIV test reports in ethnic groups in Canada, it is very important to consider some of the following, which may affect the usefulness of ethnicity reporting:

• Reporting of ethnicity is not complete for either reported AIDS cases or positive HIV test reports. Since the beginning of reporting to the end of the year 2001, approximately 15% of reported AIDS cases and 93% of positive HIV test reports in the national AIDS and HIV surveillance system did not contain information on ethnicity.
• People may not wish to identify their ethnicity. This will result in under-representation. This means that the number of individuals who accurately identify their ethnicity may not be the only people who should be in that category. Therefore, the number of people reported in an ethnic category may not be the true number in that category.
• In AIDS case reporting, patients and health care providers are currently limited to six ethnic categories and one "Other" category listed on the AIDS Case Report Form. As one must choose from this defined list, the choices could be restricted, which may affect the accuracy of ethnicity reporting.
• Variations in the completeness of ethnicity reporting within and among provinces and territories may result in under- or over-representation of HIV infection among specific ethnic groups.
  

EXPOSURE CATEGORY
(See also FAQs 1-3, 8)

In HIV/AIDS surveillance, exposure category refers to the most likely way a person became infected with the HIV virus, that is, the most likely route through which HIV was transmitted to that person.

A person may report many or no risk factors for HIV. Even though all risk factors associated with a positive HIV test result are included in the positive HIV test report and entered into the national HIV/AIDS database, only one exposure category is assigned to a positive HIV test report for national HIV/surveillance reporting. A person reporting many HIV-related risk factors will be placed in the exposure category corresponding to the activity or situation that is considered to have the highest risk of HIV transmission of the risk factors reported.

For example, Jeff explains to the health care provider ordering his HIV test that he injects drugs and also that, on occasions, he has not used a condom when having sex with his female sexual partner, who is infected with HIV. As injecting drug use is considered to be the higher risk activity according to the accepted exposure category hierarchy, Jeff's exposure category would therefore be recorded and reported as an injecting drug user (IDU). As another example: Nathan explains to the health care provider ordering his HIV test that he injects drugs and also that, on occasions, he has not used a condom when having sex with his male sexual partner, who is infected with HIV. In HIV/AIDS surveillance reporting, the risk behaviours of injecting drug use and being a man who has had sex with other men are considered to carry equal risk of HIV. Nathan's exposure category would therefore be recorded and reported as MSM/IDU.

The exposure categories used in Canadian HIV/AIDS surveillance and reporting are explained below:

• MSM
  Men who report having had sex with men; this includes men who report either homosexual or bisexual contact (i.e. some will also report having had sex with women as well). It is important to note here that this exposure category refers to sexual behaviour and not a person's self-identified sexual identity.

• MSM/IDU
  Men who have had sex with men and have injected drugs.

• IDU
  People who inject drugs, also called injecting drug users. The acronym IDU is also often applied to the behaviour of injecting drug use, or what is also commonly referred to as injection drug use.

• Blood/Blood Products
  (a) Recipient of Blood/Blood Products: Before 1998, it was not possible to separate this combined exposure category. However, where possible after 1998 it has been separated into subcategories (b) and (c).
  
  (b) Recipient of Blood: Received transfusion of whole blood or blood components, such as packed red cells, plasma, platelets or cryoprecipitate.
  
  (c) Recipient of Clotting Factor: Received pooled concentrates of clotting factor VIII or IX for treatment of hemophilia/coagulation disorder.

• Heterosexual Contact/Endemic
  Before 1998, this was a combined exposure category but has since been separated into two subcategories:
  
  (a) Origin from a Pattern II Country: People who were born in a country in which the predominant means of HIV transmission is heterosexual contact;
  
  (b) Sexual Contact with a Person at Risk: People who report heterosexual contact with a person who is either HIV-infected or who is at increased risk for HIV infection.
  
  A person at increased risk for HIV infection would be considered in this case to include someone who is an injecting drug user, a bisexual man, a person born in a country in which the predominant means of HIV transmission is heterosexual contact, a person with hemophilia/ coagulation disorder, or a person with suspected HIV infection or AIDS.

• NIR-HET
  If heterosexual contact is the only risk factor reported and nothing is known about the HIV-related risk factor(s) associated with the partner, the case would be classified as No Identified Risk-Heterosexual (NIR-HET).

• Occupational Exposure
  Exposure to HIV-contaminated blood or body fluids, or concentrated virus in an occupational setting.

• Other
  Used to classify a person whose mode of HIV transmission is known but who cannot be classified into any of the major exposure categories listed.

• NIR (No Identified Risk)
  Where the history of exposure to HIV through any of the other categories is unknown, or there is no reported history. This exposure category may include:
  
  
  • people who are currently being followed up by their local health department;
  • people whose exposure history is incomplete because they have died;
  • people whose exposure history is incomplete because they declined to be interviewed or were lost to follow-up; and
  • people who cannot identify any mode of transmission.

• Exposure Category Not Reported
  In certain provinces, it is not possible to report information regarding exposure category. In these situations, people are classified as Exposure Category Not Reported. This category is used only for positive HIV test reports.

• Perinatal Transmission
  The transmission of HIV from an HIV-infected mother to her child either
  
  
  • during pregnancy,
  • during labour,
  • at birth, or
  • after birth through breastfeeding.
    
    
  It should be noted that the term "mother-to-child-transmission" (MTCT) is also used to describe transmission of HIV from an HIV-infected mother to her child.

EXPOSURE CATEGORY HIERARCHY
(See also FAQs 1, 3)

Reported AIDS cases and positive HIV test reports are assigned to a single exposure category according to a hierarchy of HIV-related risk factors. The exposure or HIV-related risk factor considered to carry the highest risk of HIV infection is listed at the top of the hierarchy, and the exposure or HIV-related risk factor considered to carry the lowest risk of HIV infection is listed at the bottom of the hierarchy.

The exposure category hierarchy is used to determine the one exposure category that will be recorded for each positive HIV test report and each reported AIDS case. If more than one risk factor is reported, the case is classified in the exposure category listed first (or highest) in the hierarchy.

The exposure category hierarchy is currently under review to ensure that it reflects the most up-to-date information on HIV transmission risk.

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