For additional terms and definitions, visit the CTN CIHR Candian HIV Trials Network‘s website.


Co-infection is the simultaneous invasion of the body by two pathogens. In this study, the term co-infection is referring to the presence of the human immunodeficiency and hepatitis C viruses in the body at the same time.


A cohort is any designated group of people who are followed or traced over a period of time. For example, all of the students in a class, everyone born in Canada in 1984 or a group of individuals participating in a study.

Cohort study

A cohort study is an observational study in which a group of subjects are followed over time. Information is collected about the subjects' characteristics and exposures and then they are followed to see which subjects experience the health outcome of interest. For example, the outcome of interest could be a heart attack, cancer or liver disease. The number of people who experienced the outcome is compared between those who were exposed to a factor and those who were not exposed. For example, the exposure of interest may be alcohol, a medication or high cholesterol. It is very important that the investigator is not involved in choosing whether or not a subject is exposed, and instead only observes what happens.

End-stage liver disease (ESLD)

End-stage liver disease occurs when the liver has minimal function. The only treatment for ESLD is liver transplantation.

Hepatic fibrosis

Hepatic fibrosis refers to the accumulation of scar tissue in the liver. The scar tissue is the result of repair after injury due to infection, alcohol consumption, toxins or other factors.

Hepatic steatosis

Hepatic steatosis refers to the accumulation of excess fat in the liver.

Hepatitis C (HCV)

Hepatitis C is an RNA virus that is transmitted through blood and attacks the liver. Those who are infected often do not show symptoms for a long time. It is possible for the body to clear the virus however, those who have a weakened immune system are less likely to do so. Chronic infection with HCV may lead to scarring of the liver, liver cancer or liver failure.

Highly active antiretroviral therapy (HAART)

Highly active antiretroviral therapy was introduced in the mid-1990's and consists of a combination of at least 3 antiretroviral medications; 2 nucleoside reverse transcriptase inhibitors (NRTIs) plus either a non-nucleoside reverse transcriptase inhibitor (NNRTI) or a protease inhibitor (PI).

Human immunodeficiency virus (HIV)

Human immunodeficiency virus is a retrovirus that is transmitted through blood, semen, vaginal fluids and breast milk. HIV attacks the immune system and causes Acquired Immune Deficiency Syndrome (AIDS).

Opportunistic infection

An opportunistic infection or disease occurs when pathogens that are normally fought off by a person's immune system cause illness because the person's defenses are weakened by such factors as poor nutrition or infection by HIV.