Background HIV prevalence among female sex workers (FSW) in various districts of Andhra Pradesh (AP), Karnataka (KA), Maharashtra (MH), Tamil Nadu (TN) ranged between 8 and 26%, 10 and 34%, 6 and 38%, 2 and 13%, respectively, in 2005–2006. The duration of selling or buying sex has been suggested as a key determinant that may explain ecological difference in HIV prevalence. Thus, we estimated FSW duration across geographically distinct districts and assessed its impact on HIV transmission.
Methods Cross-sectional FSW survey data from 23 districts of MH, TN, KA, AP (2005–2006) (IBBA), collected as part of the evaluation of Avahan, the India AIDS initiative, were used to estimate FSW duration (crude duration=difference between age at survey and age of entry into sex work). “Corrected” durations that adjust for the censored nature of the data (as FSW are still in sex work) were estimated for FSW using a birth-and-death dynamical model (with 9 duration compartments) fitted by maximum likelihood to each district-specific FSW IBBA duration distribution. A deterministic model of HIV transmission among FSW/clients was parameterized/fitted to Belgaum IBBA data with crude FSW duration of 9.6 years for FSW. FSW duration was thereafter varied between 1and 33 years to assess its influence on model HIV prevalence, for different assumed client duration (4–17 years). Each individual leaving was replaced by a new susceptible person.
Results Mean crude FSW durations ranged between 3.7 and 9.6 (median 3–7) years across districts compared to 4.3 (Bangalore, Thane street-based) and 12.5 (Belgaum) after correction. District average corrected durations tended to be shorter for TN (6 years) and longer for MH (9 years). Within-district differences (ratios) between corrected and crude durations ranged between 0.5 and 3 years (1.1–1.3-fold). Observed differences in FSW duration across districts had a modest impact on FSW/client HIV prevalence if duration exceeded 9 years (Abstract P2-S2.16 figure 1), independently of client duration. The impact of FSW duration below 3 years on FSW/client HIV was critical. FSW/client HIV prevalence was more sensitive to variation in client duration exceeding 9 years (Abstract P2-S2.16 figure 1).
Conclusions Crude duration may underestimate FSW duration by up to 32%. This level of error is unlikely to influence FSW HIV prevalence projections. Large variation in HIV across districts is unlikely to be explained by FSW duration alone if exceeding 9 years but could be potentially be explained by variation in client duration.