Concurrency, sexual networks and HIV/AIDS

The debate about the role of concurrent sexual partnerships in the spread of HIV is influenced by weak/limited empirical data on concurrency.

Longitudinal data (n = 2958) were employed to examine the prevalence of individual concurrency (someone who has additional partners) and perceived partner concurrency (partner perceived to have additional partners) by population group and gender in 2005 and 2009. Fixed effects logit regression models were created to examine factors associated with changes in individual concurrency.

The prevalence of individual concurrency increased among black men (from 33% in 2005 to 39% in 2009), remained constant among black women (14%), decreased among coloured men (from 16% to 8%) and remained low among coloured women (2% in 2005 and 1% in 2009). Overall, a small decrease in perceived partner concurrency was observed. Changes in individual concurrency were positively associated with changes in perceived partner concurrency and finding employment; and negatively associated with household income.

Race and gender differences in concurrency should be taken into account in future research and HIV-prevention initiatives. High and increasing levels of concurrency within most recent partnerships among black men highlight this group as a potential focus for such efforts.

Empirical estimates of the female-to-male sex ratio of infections in generalized HIV epidemics in sub-Saharan Africa range from 1.31 in Zambia to 2.21 in Ivory Coast. Gender inequalities in the sex ratio of infections can arise because of differences in exposure (to HIV positive partners), susceptibility (given exposure), and survival (once infected). Differences in susceptibility have to date received most attention, but neither the relatively high sex ratio of infections nor the heterogeneity in the empirical estimates in generalized epidemics is fully understood. In this contribution we focus on partnership network attributes and sexual mixing patterns that could lead to gender differences in the exposure to HIV positive partners. Using agent-based simulations, we show that gender asymmetric partnership concurrency, rapid partnership turnover, elevated partnership dissolution in female positive serodiscordant couples and lower partnership re-entry rates among HIV positive women can produce (substantial) differences in the sex ratio of infections. Coital dilution and serosorting have modest moderating effects.

A large body of research has found that sexual partner concurrency increases the transmission of sexually transmitted infections, including HIV. Researchers are now calling for further investigation into the types of concurrency that promote or impede onward transmission of STIs. In this paper, we use life history data collected from youth in urban Kisumu, Kenya, to examine levels of protection within concurrencies, defined by combinations of sexual intercourse and condom use. We find that approximately one-third of concurrency episode months were completely protected by consistent condom use and/or no sexual intercourse, and thus the large majority of months were not protected and therefore at some risk of STI transmission. Regression results show that mutual concurrency is more likely to display full protection for females and longer concurrencies, which are thought to increase transmission potential, are more likely to be protected among both females and males.

Concurrent partnerships are often considered a primary driver of the HIV epidemic in Sub-Saharan Africa. Due to data constraints, however, few studies have been able to demonstrate its effect using empirical data. In this paper, we test whether HIV transmission rates are higher for individuals with concurrent partners - an effect that is ascribed to the higher viral load shortly after seroconversion. Data spanning a 14-year time period are pooled from two rural community sero-surveillance sites in south-Western Uganda. Sero-concordant negative married couples are followed over time, examining the risk of seroconversion for couples exposed to concurrency. A discrete-time hazard model is used to determine the risk of seroconversion among women whose husbands reported a concurrent partnership. We are unable to detect an effect of the husband’s concurrency on the HIV incidence of their wives. Our preliminary findings are in support of a growing body of literature that casts doubt on the role of concurrency for the spread of HIV.