UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Making HIV Prevalence and AIDS Estimates UNAIDS/WHO Working Group on Global HIV/AIDS and STI Surveillance

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance HIV/AIDS: Data Needs What are the levels and trends in HIV infection? Who is getting infected? Who is more at risk for or vulnerable to HIV infection? Impact assessment (need for care, planning) Is the response effective?

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Courtesy of Thomas Rehle, Family Health International

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance UNAIDS/WHO Classification of epidemic states LOW LEVEL: HIV prevalence has not consistently exceeded five percent in any defined sub-population CONCENTRATED HIV prevalence consistently over five percent in at least one defined sub-population but below one percent in pregnant women in urban areas. GENERALISED HIV prevalence consistently over one percent in pregnant women nation-wide

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Three Steps in Making Estimates Calculating HIV Prevalence Curve Fitting Generating other variables (e.g., mortality, incidence)

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Calculating HIV prevalence: Industrialized Countries AIDS Back-calculation Statistical method that allows estimating the past HIV incidence required to provide the present level of AIDS cases, corrected by underreporting Curve fitting of past incidence HIV Incidence estimates HIV case reporting Incidence studies using “detuned” ELISA

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Two different sets of procedures for: low-level and concentrated epidemics HIV is concentrated mainly in sub-populations which may vary from country to country (e.g., IV drug users, CSW, MSM) generalized epidemics HIV has spread widely in the adult population primary mode of transmission is heterosexual Calculating HIV prevalence: Developing Countries

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Calculating HIV prevalence: Concentrated Epidemics Estimates are made by adding together: the number of individuals assumed to be infected in each identifiable sub- population at risk. a minimum estimate of HIV infection in the general population

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Identify risk groups Estimate size of groups Estimate HIV prevalence in risk groups Estimate HIV prevalence in the general population Sum of all groups Calculating HIV prevalence: concentrated and low-level epidemics

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Estimating Prevalence in a Concentrated Epidemic Assumptions: MSM population: Used 2% of adult men for low and 4% for high MSM Prevalence Rate Used 1995 prevalence data (15%), with 10% for low and 20% for high STI Population Used 1% of adult as low, 2% as high. Assume higher rates among men STI Prevalence Rate sentinel surveillance = 4.3%, used 3.3 as low and 5.3 as high General Population: Used 2000 UN population numbers for minus the risk groups General population prevalence Based on anc sentinel data (0.55%). Used adjustment for rural, then had 0.1% for low, and 0.3% for high

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Estimating Prevalence in a Concentrated Epidemic Population Population Size High Population Size Low Percent Infected High Percent Infected Low Low-Low Estimate Low-High Estimate High-Low Estimate High-High Estimate IVDU700, , , ,640 54, ,000 CSW Promiscuous People502, , ,023 People with STI565, , ,055 4,746 General (15-49)23,345,698 24,366, ,056 28,015 Total25,113,000 37, ,128 73, ,784 Assumptions: IVDU Population SizeUsed high estimate from Karl's paper (and close to 6% of males) and 2% of males as low (see table below) IVDU Prevalence RateUsed High from Lev's study in Odessa, and a low from Karl's registered IVDU's CSW * P.P. PopulationUsed 2% of population for CSW/Promiscuous and.5% for low estimate CSW Prevalence RateUsed CSW prevalence rate from Karl's paper as high, half of that (overlap with IVDU) as low STI PopulationUsed 15 times reported syphilis rate as high, and 10 times reported rate as low STI Prevalence RateUsed 50% higher than reported (Karl's paper) as high prevalence, 50% lower, as low General Population:Used 98 UN population numbers for minus the risk groups General population prevalenceUsed anc rates for high and blood donors for low estimate

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Calculating HIV prevalence: Generalized Epidemics Prevalence estimates are based primarily on surveillance data collected from women attending antenatal clinics. Two groups of clinics based on their location major urban areas outside major urban areas median prevalence rates are calculated separately for the two groups

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Calculating Prevalence 1.Determine median of urban and outside major urban sites 2. Adjust medians based on representativeness of sites 3. Apply adjusted rates to female urban and outside urban populations (15-49) 4.Use M/F ratio to determine number of men infected 5. Combine males and females to get adult rate

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Critical Issues in Estimating Prevalence Representativeness of ANC sites Effects of HIV infection on fertility Male-to-female ratio Urban to rural prevalence differential

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Representativeness of ANC: Other Factors Age-related fertility reduction in HIV positive women Changes in risk behaviors (condom use, contraception) “Active aging” (risk beyond reproductive ages) Selection and participation bias (users fees, availability/access to ANC services) These factors have been identified for further study but are not considered in the present methodology

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Representativeness of ANC for total Population: Male/Female Differentials Population-based HIV prevalence in men and women - Lusaka, Zambia, 1995

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Assessing Urban/Rural Differentials: Surveillance Data for Kenya

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Comparison of HIV Prevalence Among Pregnant Women and All Adults LusakaMposhiMwanzaRakai-90Rakai-91Rakai-92Kisumu ANC Pop

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Three Steps in Making Estimates Calculating HIV Prevalence Curve Fitting Generating other variables (e.g., mortality, incidence)

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Curve Fitting Epimodel was used to fit a curve to yearly estimates of adult prevalence. Not designed to make HIV projections. Not designed to fit prevalence curves Limited to the gamma curve May not suitable for slowly progressing epidemics (Asia) New curve-fitting software is being developed

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance EPIModel Developed by WHO/GPA Tool for making short-term projections of AIDS cases, AIDS mortality, paediatric AIDS and AIDS orphans. NOT DESIGNED to make estimates or projections of prevalence of HIV infections

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Curve Fitting Point prevalence estimates (at least one, the more the better!) Year of initial spread Assumptions about peak of the epidemic Post-peak curve assumptions

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Year URBANOUTSIDEMED-URBAN MED-OUTSIDEUNAIDS/WHO adult prevalence curve HIV Prevalence for Pregnant Women Major Urban and Outside Major Urban Areas Zambia

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Three Steps in Making Estimates Calculating HIV Prevalence Curve Fitting Generating other variables (e.g., mortality, incidence, orphans)

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Generating Other Variables Epimodel (or the new model) is used to generate additional information on Incidence Vertical transmission Mortality (adult and child) Orphans

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Generating Other Variables: information needed Population size (15-49) Progression rates from infection to death Age specific fertility rates Fertility reduction for HIV Male-to-female ratio Mother-to-child transmission rate

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Age-specific information about population and fertility United Nations Population Division estimates: age-specific fertility rates population figures

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Generating Other Variables Progression Rates Infection to death for adults Median 9 years in countries with poor health care Median 11 years in countries with better health care Infection to death for children Median 2 years in countries with poor health care Median 4 years in countries with better health care

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Progression Rates Child Survival Rates Years since infection Percent surviving Slow Fast Adult Survival Rates Years since infection Percent surviving Fast Slow

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Estimating Vertical Transmission Male to female ratio Fertility rate Fertility reduction for HIV+ Vertical transmission rate (25%  10%) Impact of ARV prophylaxis on MTCT

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Mortality estimates Due to the limitations in vital registration and case reporting, AIDS deaths are derived from the estimated HIV prevalence curve and the progression rate from infection to AIDS and death Pre-AIDS mortality (deaths in HIV infected adults and children due to other causes unrelated to HIV) is deducted from the total mortality estimate

UNAIDS/WHO Working Group on Global HIV/AIDS/STI Surveillance Projections He who predicts the future lies, even if he is telling the truth! Predictions are very difficult, particularly when the future is concerned.