Sexually transmitted infections: unravelling transmission & impact

The aim of the thesis was to gain insight into sexual mixing patterns, the effect of these patterns on the spread of sexually transmitted infections (STIs), pathogen interactions, and infectious disease progression and outcome.
The main findings are:
1. Among heterosexuals in Amsterdam, partnership factors (e.g. age difference) are more important determinants of unprotected sexual contact than characteristics of the individual. STI prevalence differences between ethnic populations are not always caused by differences in sexual behaviour.
2. Demographic characteristics (e.g. age) are less important for partner selection among men who have sex with men (MSM); the key determinant of unprotected anal intercourse among MSM is perceived concordant HIV status. Molecular epidemiology of Chlamydia trachomatis and N. gonorrhoeae did not reveal subpopulations among MSM, suggesting a homogeneously mixed population, but the risk to acquire N. gonorrhoeae differed between meeting venues. Furthermore, the pharynx is more important for the spread of N. gonorrhoeae than the rectum, even though the prevalence of rectal infections is higher.
3. The disease burden of hepatitis C virus infection will increase in the upcoming years among people who inject drugs. HCV treatment will reduce the burden, but postponing implementation of treatment reduces its effect, because the population becomes older and the average duration of infection is increasing.
4. Finally, no evidence for a reduction in mortality from HIV-1 in individuals dually infected with HIV-1 and HIV-2 in West Africa was found.
We are entering a new era in which biomedical prevention strategies become important. In response, pathogen dynamics are likely to change.