Evaluating two adjustment methods to extrapolate HIV prevalence from pregnant women to the general female population in sub-Saharan Africa

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Abstract
To evaluate two methods for estimating HIV prevalence among the general female population of reproductive age by adjusting data observed among antenatal clinic (ANC) attendees. We adjusted the HIV prevalence among ANC attendees in Fort Portal (Uganda; 1994-1995), Mwanza municipality (Tanzania; 1990-1991), rural Mwanza (Tanzania; 1991-1993), Mposhi district (Zambia; 1994), Chelston (Lusaka, Zambia; 1994, 1996 and 1998) and Ndola (Zambia; 1998), using firstly a method that accounts for differences in age-specific fertility by HIV serostatus and secondly a method that accounts for differences in HIV prevalence by fertility risk category and parity. The non-adjusted HIV prevalence among ANC attendees underestimates the prevalence among the general female population by 8.0% in Chelston in 1998 and by between 20.7% and 31.9% in all other cases. The adjusted prevalence obtained using the first method underestimates the prevalence among the general female population by about 0.5% in Fort Portal and Mposhi; it overestimates that observed in Chelston in 1994 and 1996 by about 3.5%, and that observed in Ndola, urban Mwanza and rural Mwanza, by 6.5%, 10.6% and 12.8%, respectively. The second method (applied for only four sites) provides an overestimate of 7.0% in Chelston in 1994 and an underestimate of 3.8% and 2.1% in Ndola and rural Mwanza, respectively. Both adjustment methods overestimate the 1998 prevalence in Chelston, producing less accurate estimates than the non-adjusted data. The HIV prevalence among women in the general population could be estimated fairly accurately by these methods in settings with mature epidemics.