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Measuring the HIV/AIDS epidemic

Measuring the HIV/AIDS epidemic. Prevalence Incidence. Prevalence. Prevalence is: the % of a population infected with HIV at a point in time Prevalence = no. of people with HIV X 100 total population. Prevalence. Provides a “snapshot” of the situation

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Measuring the HIV/AIDS epidemic

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  1. Measuring the HIV/AIDS epidemic • Prevalence • Incidence

  2. Prevalence Prevalence is: the % of a population infected with HIV at a point in time Prevalence = no. of people with HIV X 100 total population

  3. Prevalence • Provides a “snapshot” of the situation • Usually used to measure chronic diseases • Includes both old and new infections • Does not show recent trends

  4. Incidence Incidence is: the number of new HIV infections occurring in a population over a period of time Incidence = no. of people newly infected with HIV over 1 year total population

  5. Incidence • Measures how quickly an epidemic is spreading • Usually used to measure acute diseases

  6. Incidence or prevalence for HIV? • Prevalence is mostly used to measure HIV • HIV incidence is difficult to measure • In young people: HIV prevalence used as proxy measure for incidence - new trends in epidemic

  7. Measuring prevalence • Population - based surveys • Sentinel populations: - Antenatal clinics - Blood donors (trends) - STI clinic clients (trends)

  8. Measuring HIV prevalence Anonymous unlinked testing: • Blood sample usually taken for other purposes • All identifying markers removed • Individual does not receive result • Consent is not required

  9. Importance of knowing prevalence • Indication of overall scale of problem • Necessary for: • planning of services • resource allocation • advocacy • public awareness • Changes in prevalence over time can show impact of interventions

  10. Classification of HIV epidemics Low-level epidemic: Prevalence  5% in any defined subpopulation Concentrated epidemic: Prevalence > 5% in one subpopulation Prevalence < 1% in pregnant women (urban) Generalized epidemic: Prevalence > 1% in pregnant women

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