Epidemiology of HIV/AIDS

The study of how HIV and AIDS are distributed across populations, how transmission occurs, which factors shape risk, and how patterns change over time.

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HIV transmission: The passage of human immunodeficiency virus between people through specific bodily fluids and routes. Transmission routes explain the mechanisms behind population-level patterns of new infections.
Incidence: The rate at which new cases of a condition arise in a population over time. HIV incidence tracks the pace of new infections rather than the total living with HIV.
HIV treatment as prevention: The use of HIV treatment to reduce transmission by suppressing viral load in people with HIV. Population treatment coverage can lower transmission as well as improve health.
HIV incidence versus prevalence: The distinction between the rate of new HIV infections and the proportion of people living with HIV. A place can have high prevalence but falling incidence when treatment extends survival.
Sexual transmission of HIV: The transmission of HIV through sexual contact involving exposure to infectious bodily fluids. Sexual contact accounts for a large share of infections in many epidemics.
Prevalence: The proportion of a population that has a condition at a specified time or period. HIV prevalence reflects both new infections and how long people survive with HIV.
Undetectable equals untransmittable: The finding that people who maintain an undetectable HIV viral load do not sexually transmit HIV. U=U connects treatment outcomes to changes in sexual transmission risk.
HIV risk groups: Population groups with differing probabilities of HIV exposure or infection due to social and behavioral conditions. Risk patterns reflect exposure and structural conditions, not fixed biological categories.
Vertical transmission of HIV: The transmission of HIV from a pregnant person to a child during pregnancy, birth, or breastfeeding. This route produces distinct age patterns and can be reduced by treatment.
HIV testing: Tests used to detect HIV infection or evidence of the body's response to it. Testing coverage affects case counts and estimates of undiagnosed infection.