title: Assessment of the population-level effectiveness of the Avahan HIV-prevention programme in South India: a preplanned, causal-pathway-based modelling analysis.
abstract: BACKGROUND
  Avahan, the India AIDS initiative of the Bill & Melinda Gates Foundation, was a large-scale, targeted HIV prevention intervention. We aimed to assess its overall effectiveness by estimating the number and proportion of HIV infections averted across Avahan districts, following the causal pathway of the intervention.
  
  
  METHODS
  We created a mathematical model of HIV transmission in high-risk groups and the general population using data from serial cross-sectional surveys (integrated behavioural and biological assessments, IBBAs) within a Bayesian framework, which we used to reproduce HIV prevalence trends in female sex workers and their clients, men who have sex with men, and the general population in 24 South Indian districts over the first 4 years (2004-07 or 2005-08 dependent on the district) and the full 10 years (2004-13) of the Avahan programme. We tested whether these prevalence trends were more consistent with self-reported increases in consistent condom use after the implementation of Avahan or with a counterfactual (assuming consistent condom use increased at slower, pre-Avahan rates) using a Bayes factor, which gave a measure of the strength of evidence for the effectiveness estimates. Using regression analysis, we extrapolated the prevention effect in the districts covered by IBBAs to all 69 Avahan districts.
  
  
  RESULTS
  In 13 of 24 IBBA districts, modelling suggested medium to strong evidence for the large self-reported increase in consistent condom use since Avahan implementation. In the remaining 11 IBBA districts, the evidence was weaker, with consistent condom use generally already high before Avahan began. Roughly 32700 HIV infections (95% credibility interval 17900-61600) were averted over the first 4 years of the programme in the IBBA districts with moderate to strong evidence. Addition of the districts with weaker evidence increased this total to 62800 (32000-118000) averted infections, and extrapolation suggested that 202000 (98300-407000) infections were averted across all 69 Avahan districts in South India, increasing to 606000 (290000-1 193000) over 10 years. Over the first 4 years of the programme 42% of HIV infections were averted, and over 10 years 57% were averted.
  
  
  CONCLUSIONS
  This is the first assessment of Avahan to account for the causal pathway of the intervention, that of changing risk behaviours in female sex workers and high-risk men who have sex with men to avert HIV infections in these groups and the general population. The findings suggest that substantial preventive effects can be achieved by targeted behavioural HIV prevention initiatives.
  
  
  BACKGROUND
  Bill & Melinda Gates Foundation.
authors.affiliation: School of Public Health, Imperial College London, London, UK; Social and Mathematical Epidemiology Group, Department of Global Health and Development, London School of Hygiene & Tropical Medicine, London, UK.
authors.forename: Michael
authors.initials: M
authors.lastname: Pickles
authors.affiliation: School of Public Health, Imperial College London, London, UK. Electronic address: mc.boily@imperial.ac.uk.
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Boily
authors.affiliation: Social and Mathematical Epidemiology Group, Department of Global Health and Development, London School of Hygiene & Tropical Medicine, London, UK; Department of Social Medicine, University of Bristol, Bristol, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Vickerman
authors.affiliation: Social and Mathematical Epidemiology Group, Department of Global Health and Development, London School of Hygiene & Tropical Medicine, London, UK; Public Health England, London, UK.
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Lowndes
authors.affiliation: Department of Community Health Sciences, University of Manitoba, Winnipeg, MB, Canada; Karnataka Health Promotion Trust, Bangalore, India.
authors.forename: Stephen
authors.initials: S
authors.lastname: Moses
authors.affiliation: Department of Community Health Sciences, University of Manitoba, Winnipeg, MB, Canada; Department of Medical Microbiology, University of Manitoba, Winnipeg, MB, Canada.
authors.forename: James F
authors.initials: JF
authors.lastname: Blanchard
authors.affiliation: School of Population and Public Health, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Kathleen N
authors.initials: KN
authors.lastname: Deering
authors.affiliation: CHARME-India Project, Bangalore, India; Unité de Recherche en Santé des Populations, Centre de Recherche du CHU de Québec, Département de Médecine Sociale et Préventive, Faculté de Médecine, Université Laval, QC, Canada.
authors.forename: Janet
authors.initials: J
authors.lastname: Bradley
authors.affiliation: Karnataka Health Promotion Trust, Bangalore, India.
authors.forename: Banadakoppa M
authors.initials: BM
authors.lastname: Ramesh
authors.affiliation: Department of Community Health Sciences, University of Manitoba, Winnipeg, MB, Canada; St John's Medical College and Hospital, Bangalore, India.
authors.forename: Reynold
authors.initials: R
authors.lastname: Washington
authors.affiliation: FHI 360, Washington, DC, USA.
authors.forename: Rajatashuvra
authors.initials: R
authors.lastname: Adhikary
authors.affiliation: National AIDS Research Institute, Pune, India.
authors.forename: Mandar
authors.initials: M
authors.lastname: Mainkar
authors.affiliation: National AIDS Research Institute, Pune, India.
authors.forename: Ramesh S
authors.initials: RS
authors.lastname: Paranjape
authors.affiliation: Unité de Recherche en Santé des Populations, Centre de Recherche du CHU de Québec, Département de Médecine Sociale et Préventive, Faculté de Médecine, Université Laval, QC, Canada; Institut National de Santé Publique du Québec, Québec City, QC, Canada.
authors.forename: Michel
authors.initials: M
authors.lastname: Alary
mesh_terms: D003430:Cross-Sectional Studies; D005260:Female; D015658:HIV Infections / Q000453:epidemiology / Q000517:prevention & control* / Q000635:transmission; D006293:Health Promotion / Q000592:standards*; D018451:Homosexuality, Male; D006801:Humans; D007194:India / Q000453:epidemiology; D008297:Male; D015233:Models, Statistical; D015397:Program Evaluation / Q000379:methods; D012044:Regression Analysis; D060386:Sex Workers