Interim modelling analysis to validate reported increases in condom use and assess HIV infections averted among female sex workers and clients in southern India following a targeted HIV prevention programme.

Objectives: This study assesses whether the observed declines in HIV prevalence since the beginning of the 'Avahan' India HIV/AIDS prevention initiative are consistent with self-reported increases in condom use by female sex workers (FSWs) in two districts of southern India, and provides estimates of the fraction of new infections averted among FSWs and clients due to increases in condom use in commercial sex after 2004.

Methods: A deterministic compartmental model of HIV/sexually transmitted infection (STI) transmission incorporating heterogeneous sexual behaviour was developed, parameterised and fitted using data from two districts in Karnataka, India. Three hypotheses of condom use among FSWs were tested: (H(0)), that condom use increased in line with reported FSW survey data prior to the Avahan initiative but remained constant afterwards; (H(1)) that condom use increased following the Avahan initiative, in accordance with survey data; (H(2)) that condom use increased according to estimates derived from condom distribution data.