HIV/AIDS Epi Update - May 2004

Glossary

A Guide to HIV/AIDS Epidemiological and Surveillance Terms is available. Hard copies may be obtained through the Surveillance and Risk Assessment Division, whose address is listed under the "Information to Readers of HIV/AIDS Epi Updates" section. A selected number of acronyms and terms that may be useful when reading HIV/AIDS Epi Updates are listed below.

Acronyms

Terms

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 who will be participants in the study. This group of people is called a cohort.
• The cohort is followed for a specified 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 (HCV), or HIV and tuberculosis (TB), 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.

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.

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 is often used as the denominator in expressing incidence rate.

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 nfection, occurring during a specified time period.

Risk Factor

• Is 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.

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

• Is 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 sero-converter.

Seroprevalence

• The terms refers to the prevalence or prevalence rate of a disease determined by testing blood rather than saliva, urine or sputum.

Surveillance

• Is 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.

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