title: Acute-stage transmission of HIV: effect of volatile contact rates.
abstract: BACKGROUND
  The role of acute-stage transmission in sustaining HIV epidemics has been difficult to determine. This difficulty is exacerbated by a lack of theoretical understanding of how partnership dynamics and sexual behavior interact to affect acute-stage transmission. We propose that individual-level variation in rates of sexual contact is a key aspect of partnership dynamics that can greatly increase acute-stage HIV transmission.
  
  
  METHODS
  Using an individual-based stochastic framework, we simulated a model of HIV transmission that includes individual-level changes in contact rates. We report both population-level statistics (such as prevalence and acute-stage transmission rates) and individual-level statistics (such as the contact rate at the time of infection).
  
  
  RESULTS
  Volatility increases both the prevalence of HIV and the proportion of new cases from acute-stage infectors. These effects result from 1) a relative reduction in transmission rate from chronic but not acute infectors and 2) an increase in the availability of high-risk susceptibles.
  
  
  CONCLUSIONS
  The extent of changes in individual-level contact rates in the real world is unknown. Aggregate or strictly cross-sectional data do not reveal individual-level changes in partnership dynamics and sexual behavior. The strong effects presented in this article motivate both continued theoretical exploration of volatility in sexual behavior and collection of longitudinal individual-level data to inform more realistic models.
authors.affiliation: Department of Epidemiology, University of Michigan, Ann Arbor, MI 48104, USA. eoromero@umich.edu
authors.forename: Ethan Obie
authors.initials: EO
authors.lastname: Romero-Severson
authors.forename: Shah Jamal
authors.initials: SJ
authors.lastname: Alam
authors.forename: Erik
authors.initials: E
authors.lastname: Volz
authors.forename: James
authors.initials: J
authors.lastname: Koopman
mesh_terms: D000208:Acute Disease; D015658:HIV Infections / Q000453:epidemiology / Q000635:transmission*; D006801:Humans; D008954:Models, Biological; D015995:Prevalence; D012725:Sexual Behavior / Q000706:statistics & numerical data*