title: HIV transmission from drug injectors to partners who do not inject, and beyond: modelling the potential for a generalized heterosexual epidemic in St. Petersburg, Russia.
abstract: BACKGROUND
  HIV infection is prevalent among drug injectors in St. Petersburg and their non-injecting heterosexual partners (PIDUs). There are fears that sexual transmission of HIV from IDUs to PIDUs may portend a self-sustaining, heterosexual epidemic in Russia.
  
  
  METHODS
  Our model combines a network model of sexual partnerships of IDUs and non-IDUs to represent sexual transmission of HIV and a deterministic model for parenteral transmission among IDUs. Behavioural parameters were obtained from a survey of St. Petersburg IDUs and their sexual partners. We based our model fits on two scenarios for PIDU prevalence in 2006 (5.6% and 15.1%, calculated excluding and including HCV co-infected PIDUs respectively) and compared predictions for the general population HIV prevalence.
  
  
  RESULTS
  Results indicate that sexual transmission could sustain a non-IDU HIV epidemic. The model indicates that general population prevalence may be greater than current estimates imply. Parenteral transmission drives the epidemic and the PIDU bridge population plays a crucial role transferring infection to non-IDUs. The model indicates that the high PIDU prevalence is improbable because of the high risk behaviour this implies; the lower prevalence is possible.
  
  
  CONCLUSIONS
  The model implies that transmission through PIDUs will sustain a heterosexual epidemic, if prevalence among IDUs and PIDUs is as high as survey data suggest. We postulate that current estimates of population prevalence underestimate the extent of the HIV epidemic because they are based on the number of registered cases only. Curtailing transmission among injectors and PIDUs will be vital in controlling heterosexual transmission.
authors.affiliation: Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London, St Mary's Campus, Norfolk Place, London W2 1PG, United Kingdom. Electronic address: harriet.l.mills@gmail.com.
authors.forename: Harriet L
authors.initials: HL
authors.lastname: Mills
authors.forename: Edward
authors.initials: E
authors.lastname: White
authors.forename: Caroline
authors.initials: C
authors.lastname: Colijn
authors.forename: Peter
authors.initials: P
authors.lastname: Vickerman
authors.forename: Robert
authors.initials: R
authors.lastname: Heimer
mesh_terms: D058872:Epidemics / Q000706:statistics & numerical data*; D005260:Female; D015658:HIV Infections / Q000453:epidemiology / Q000635:transmission*; D020010:Heterosexuality / Q000523:psychology*; D006801:Humans; D008297:Male; D008960:Models, Psychological; D015995:Prevalence; D012426:Russia / Q000453:epidemiology; D012747:Sexual Partners / Q000523:psychology*; D015819:Substance Abuse, Intravenous / Q000453:epidemiology / Q000523:psychology*; D047568:Unsafe Sex / Q000523:psychology
keywords: Heterosexual transmission; Injecting drug users; Mathematical model; Partners of IDUs; Russia; Surveillance