ESTIMATING HIV INCIDENCE FROM AGE-SPECIFIC PREVALENCE DATA - COMPARISON WITH CONCURRENT COHORT ESTIMATES IN A STUDY OF MALE FACTORY-WORKERS, HARARE, ZIMBABWE

Objective: To compare HIV incidence estimates from cross-sectional age -specific prevalence data with concurrent cohort estimates and to exam ine the sensitivity of the estimates to changes in age-categorization and survivorship assumptions. Methods: Two previously described method s of estimating HIV incidence from cross-sectional prevalence data - t he cumulative incidence and survival (CIS) and constant prevalence (CP ) methods - are applied using data from a study of male factory worker s in Harare, Zimbabwe. The methods are applied under two alternative g roupings of the HIV prevalence data and under alternative survivorship assumptions: (a) Weibull distribution providing the best fit to the H IV prevalence data using the CIS method; (b) Weibull distribution matc hing data from an HIV natural history cohort study in Uganda; and (c) survivorship pattern as in (b) with survival periods reducing with inc reasing age at infection. Age-specific, age-standardized and cumulativ e HIV incidence estimates are calculated. The results are compared wit h concurrent longitudinal estimates from 3 years of follow-up of the H arare cohort (1993-1995). Results: Age-standardized HIV incidence was estimated at 2.02 per 100 man years (95% CI, 1.57-2.47) in the cohort study. There was evidence of recent variability in HIV incidence in th ese data. Estimates from the cross-sectional methods ranged from 1.98 to 2.74 per 100 man years and were sensitive to changes in age-categor ization of the HIV prevalence data and changes in survivorship assumpt ions. The cross-sectional estimates were higher at central ages and lo wer at older ages than the cohort estimates. The age-specific estimate s from the CIS method were less sensitive to changes in age grouping t han those from the CP method. Conclusions: HIV incidence remains high in Harare. Incidence estimates broadly consistent with cohort estimate s can be obtained from single-round cross-sectional HIV prevalence dat a in established epidemics - even when the underlying assumption of st able endemic prevalence is not fully met. Estimates based on cross-sec tional surveys should therefore be explored when reliable longitudinal estimates cannot be obtained. More data on post-HIV infection survivo rship distributions in sub-Saharan Africa would facilitate the improve ment of estimates of incidence based on cross-sectional surveys. (C) 1 998 Lippincott Williams & Wilkins.