Worst case analysis of sexual mixing models of HIV transmission

Abstract

The sexual transmission of HIV/AIDS depends upon the specifics of mixing between subpopulations with differing sexual activity rates. As the manner in which such mixing occurs is very difficult to observe, it is natural to consider the number of infected persons that would result from worst case mixing, that is, mixing that maximizes the number of infected persons in the population. This paper summarizes a recently developed procedure for producing a tight upper bound on the maximum number of infected persons in a population over the long run within the assumptions of a fairly general model of HIV transmission. The technique is illustrated utilizing parameters derived from studies of the AIDS epidemic in San Francisco. An example demonstrating how one might prospectively evaluate an AIDS intervention program using worst case analysis is also discussed.

Mathematical models for the study of HIV spread and control amongst men who have sex with men

“…The first peak is driven by a rapid spread in high-activity groups followed by a later epidemic in low-activity groups. The highest total number of infections is obtained if MSM mix proportionately by sexual activity [52,55,117] or when dualrole MSM mix primarily but not completely with themselves [61]. Within-age-group mixing may cause a lower endemic HIV prevalence in those under 25 years old because infections are prevented from spreading from the older to younger generations [66].…”

“…Two HIV incidence peaks [51,54,55,98] Sexual activity proportionate mixing Highest total number of infections over epidemic course (worst-case scenario) [52,55,117] Higher degree of sexual role assortative mixing Higher HIV prevalence [61] At some degrees of assortativity, can provide highest total number of infections over epidemic course (worst-case scenario) [61] Sexual role proportionate mixing Lower (when R0 is low) and higher (when R0 is high) total number of infections than when dual-role MSM are completely separated [61] Higher degree of age assortative mixing Lower HIV prevalence in adolescents and young adults in endemic state [66] Whether or not the ART could reduce overall transmission remains a controversial issue. Lower HIV incidence was found to have resulted from a higher ART uptake [19,32,36,70,73,74,79], particularly if started during the primary infection stage [33,48].…”

Increased attention to human sexuality can improve HIV-AIDS prevention efforts: Key research issues and directions.

“…Populations characterized by such lower stability and greater change in sexual partnerships are those in which HIV infection has become prevalent or is showing a rapid increase in incidence (Curran et al, 1988). Multiple sexual partnerships are only one of several factors that determine HIV risk; others include the type of sexual practice occurring between partners and its efficiency for transmitting HIV if one partner is infected, whether (and how consistently) condoms are used during intercourse, the base rate prevalence of HIV infection within the population segment and the corresponding likelihood of encountering infected partners, coexisting prevalence of other sexually transmitted diseases (STDs), and the nature of sexual network mixing patterns (Isham, 1988;Kaplan, 1989Kaplan, ,1991May & Anderson, 1987). Nonetheless, identification of the prevalence of multiple partnership patterns and efforts to characterize population segments and age groups that are at elevated HIV risk because of casual or brief serial relationships can guide the direction of HIV prevention efforts, whether they are intended to discourage casual relationships or to encourage consistent condom use in these relationships.…”