Measuring the HIV/AIDS epidemic

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Measuring the HIV/AIDS epidemic

• Prevalence
• Incidence

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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

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Prevalence

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

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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

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Incidence

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

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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

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Measuring prevalence

• Population - based surveys
• Sentinel populations
• - Antenatal clinics
• - Blood donors (trends)
• - STI clinic clients (trends)

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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

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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

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Classification of HIV epidemics

• Low-level epidemic
• Prevalence ? 5 in any defined
  subpopulation
• Concentrated epidemic
• Prevalence gt 5 in one subpopulation
• Prevalence lt 1 in pregnant women (urban)
• Generalized epidemic
• Prevalence gt 1 in pregnant women