PARC Working Paper Series

The structure of sexual networks and the spread of HIV in Sub-Saharan Africa: evidence from Likoma island (Malawi)

Stephane Helleringer, University of Pennsylvania
Hans-Peter Kohler, University of Pennsylvania

Document Type Working Paper

PARC Working Paper Series, WPS 06-01.


It is widely believed that the HIV epidemic in Sub-Saharan Africa (SSA) is driven by transmission during unprotected heterosexual intercourse. In particular, infection with HIV in SSA is thought to be fueled by repeated contacts with sex workers or other highly sexually active group, and subsequently diffused to the general population through links of marriage or other stable types of partnerships. Such a theoretical model of sexual mixing has informed many policy simulations of interventions to stem the spread of the disease (see Oster 2005). However, empirical evidence for this diffusion process (i.e. from a group of highly active individuals to a low activity "periphery") is somewhat scarce as epidemiological studies have generally reported weaker than expected relations between measures of such sexual behavior and risk/prevalence of HIV infection. At the individual level, differences in the rate of sexual partner acquisition only marginally predict an increased risk of infection for both prevalent (e.g. Gregson et al. 2002) and incident cases (e.g. Quigley et al. 2000). Similarly, at the population level, several comparative studies of the factors of HIV infection have found that differences in the prevalence of risky behaviors (high rate of partner change, contacts with sex workers etc.) could not explain the "uneven spread" of HIV across regions of SSA (Boerma et al. 2003). These discrepancies between indicators of sexual activity and prevalence/risk of HIV have been primarily attributed to two factors: reporting bias and differential mortality of HIV-infected individuals. Recently, they have also generated a heated debate over the relative importance of nonsexual modes of HIV transmission (e.g. unsafe medical injections) in fostering the HIV epidemic in SSA (e.g. Gisselquist et al. 2002).


Date Posted: 18 March 2008