Glossary: HIV/AIDS Epi updates, July 2010


HIV/AIDS Epi Updates - July 2010 (PDF Document - 435 KB – 11 pages)


Acquired immunodeficiency syndrome
Centre for Communicable Diseases and Infection Control
Highly Active Anti-Retroviral Therapy
Hepatitis C virus
Human immunodeficiency virus
People who inject drugs
Men who have sex with men
Needle exchange program
Public Health Agency of Canada
Sexually transmitted and blood-borne infections
Joint United Nations Programme on HIV/ AIDS
World Health Organization


Aboriginals: Aboriginals include the First Nations, Inuit and Métis people of Canada.

CD4 count: A test that indicates the strength of one's immune system and can be used to predict the risk of complications and debilitating infections. This is often used in combination with the HIV viral load test.

Cohort Study: The purpose of a cohort study is to investigate the development of new occurrences of a disease or to investigate how responses to treatment are related to specific factors. These factors can be recorded at the beginning of the study and/or during the course of the study. A cohort study starts with a group of people, identified as a cohort, who will be participants in the study. The cohort is followed for a specified time period, which can be weeks, months, years or decades. Follow-up data are collected at regularly defined periods either through the use of questionnaires, personal interviews, laboratory testing, medical examinations, or a combination of these methods. A cohort study is sometimes referred to as a prospective or longitudinal study.

Co-infection: Having two infections at the same time. For example, a person infected with both HIV and hepatitis C or HIV and tuberculosis, has a co-infection. With co-infections the progression of either disease can potentially be accelerated as a result of infection with the other disease.

Endemic: For the purposes of HIV surveillance, "HIV-endemic countries" are generally defined as those that have an adult prevalence (ages 15-49) of HIV that is 1.0% or greater and one of the following: 50% or more of HIV cases attributed to heterosexual transmission; a male to female ratio of 2:1 or less among prevalent infections; or HIV prevalence greater than or equal to 2% among women receiving prenatal care.

Exposure Category: In HIV and 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.

Highly Active Anti-Retroviral Therapy: A therapy that involves multiple anti-HIV drugs and is prescribed, before AIDS symptoms are developed, to HIV positive people.

Incidence: Incidence is the number of new events of a specific disease during a specified period of time in a specified population. HIV incidence is the number of new HIV infections occurring in a specified period of time in a specified population.

Methodology: The methodology section of a report or research study describes how the study was conducted (the methods) and the principles used by study investigators. These methods include how participants were recruited and how the data were collected, organized and analyzed.

Notifiable Disease: A disease that is considered to be of such importance to public health that its occurrence is required to be reported to public health authorities.

Perinatal Transmission: The transmission of HIV from an HIV-infected mother to her child either in utero, during childbirth, or through breastfeeding.

Person Years: Person years describes the length of time of experience or exposure of a group of people who have been observed for varying periods of time. It is the sum total of the length of time each person has been exposed, observed or at risk. You will sometimes see person years reported as PY or py. Person years are often used as the denominator in expressing incidence rate.

Pilot phase: Activity that has been organized as a trial or test period.

Population at Risk: The population at risk represents those persons at risk of contracting a disease.

Prevalence: Prevalence is the total number of people with a specific disease or health condition living in a defined population at a particular time. HIV prevalence among Canadians is the total number of people living with HIV infection (including those with AIDS) in Canada at a particular time.

Rate: A rate is an expression of the frequency with which an event occurs in a defined population in a specified period of time. In HIV/AIDS research, a rate can be the proportion of a population with a particular "event", such as HIV infection, occurring during a specified time period.

Risk Factor: An aspect of someone's behaviour or lifestyle, a characteristic that a person was born with, or an event that he or she has been exposed to that is known to be associated with a health-related condition. A behavioural risk factor describes a specific behaviour that carries a proven risk of a particular outcome. In HIV/AIDS research, you will often see the term "HIV-related risk behaviour" to describe a behaviour that, when practised, carries a proven risk of HIV infection.

Second-generation surveillance: Second generation surveillance for HIV/AIDS is the regular, systematic collection, analysis and interpretation of information for use in tracking and describing changes in the HIV/AIDS epidemic over time. Second generation surveillance for HIV/AIDS also gathers information on risk behaviours, using them to warn of or explain changes in levels of infection.

Self-Reported Data: In research studies, self-reported data is a term applied to information that is directly reported by the study participants.

Sentinel Surveillance: A type of surveillance activity in which specific facilities, such as offices of certain health care providers, hospitals or clinics across a geographic region, are designated to collect data about a disease, such as HIV infection. These data are reported to a central database for analysis and interpretation.

Seroconversion: The root "sero" means the serum of the watery portion of blood. In HIV/AIDS research, seroconversion refers to the development of detectable antibodies to HIV in the blood as a result of HIV infection. A person who goes from being HIV negative to HIV positive is said to have seroconverted or is a seroconverter.

Serodiscordant: Relationships where one partner is infected with HIV and the other is not.

Seroprevalence: The term refers to the prevalence or prevalence rate of a disease as determined by testing blood rather than saliva, urine or sputum.

Street-involved: People who are engaged in street activities (such as illict drug use, sex work, etc) that may increase their risk for HIV and STI transmission.

Surveillance: The ongoing collection, analysis and interpretation of data about a disease such as HIV or about a health condition. The objective of surveillance is to assess the health status of populations, detect changes in disease trends or changes in how the disease is distributed, define priorities, assist in the prevention and control of the disease, and monitor and evaluate related treatment and prevention programs.

Viral load: The viral load test is a quantitative measurement of HIV nucleic acid (RNA) that provides important information that is used (in conjunction with the CD4 cell count) to monitor the status of HIV disease, guide recommendations for therapy and predict the future course of the HIV infection/disease.

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