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

Abstract

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. The proportion of fits to HIV/STI prevalence data was examined to determine which hypothesis was most consistent.

Results: For Mysore 0/36/82.7 fits were identified per million parameter sets explored under hypothesis H(0)/H(1)/H(2), respectively, while for Belgaum 9.7/8.3/0 fits were identified. The HIV epidemics in Belgaum and Mysore are both declining. In Mysore, increases in condom use during commercial sex between 2004 and 2009 may have averted 31.2% to 47.4% of new HIV infections in FSWs, while in Belgaum it may have averted 24.8% to 43.2%, if there was an increase in condom use.

Discussion: Increased condom use following the Avahan intervention is likely to have played a role in curbing the HIV epidemic in Mysore. In Belgaum, given the limitations in available data, this method cannot be used alone to decide if there has been an increase in condom use.

Figure 1

Outline of the main aspects of sexual behaviour structure and population movements between risk groups that are included in the model. HIV/sexually transmitted infection (STI) transmission through main (plain arrow) and casual (dotted arrow) partnerships is shown. Female sex workers and clients engage in commercial sex for a time before returning to the general population and being replaced from the general population (thick arrow).

Figure 2

Prior parameter ranges for hypotheses H₀–H₂ reflecting the proportion of female sex workers (FSWs) who are consistently using condoms for (a) Mysore and (b) Belgaum. The upper and lower lines show the range of the prior. Also shown is the data from the historic condom reconstruction, and mean and 95% CIs for the FSW integrated behavioural and biological assessment (IBBA) values.

Figure 3

HIV prevalence over time for most likely hypothesis for (a) female sex workers (FSWs) and (b) clients in Mysore (H₂); (c) FSWs and (d) clients in Belgaum (H₀); and (e) FSWs and (f) clients in Belgaum (H₁). Shown on the graphs are median, 25th and 75th percentiles, and the 95% credibility interval (lighter shaded area). For H₁ Belgaum and H₂ Mysore the prevalence of the simulated control groups is also shown (median, 25th and 75th percentiles, and 95% credibility interval). Also shown is the integrated behavioural and biological assessment (IBBA) prevalence data.

Figure 4

Fraction of new HIV infections averted over a 5-year period from 2004 in female sex workers (FSWs) and clients as a result of increases in condom use for (A) Mysore under hypotheses H₁ and H₂ and (B) Belgaum under hypotheses H₁. Shown on the graph are the median (middle line in the box), 25th and 75th percentiles (box) and the 95% credibility interval (whiskers). Belgaum hypothesis H₀ corresponds to no impact, and is not shown.