Epidemiology of herpes and HIV co-infection

Most HIV infections are transmitted sexually, particularly in sub-Saharan Africa and Asia. In this article we review various strands of epidemiological evidence linking herpes simplex virus type 2 (HSV-2) and HIV. This includes a consideration of the similarity of the sexual risk factors and behaviours associated with acquisition of these two infections (younger age at coitarche, higher number of sexual partners, women at greater risk than men, homosexual males at greater risk than heterosexual males, previous sexually transmitted infections (STIs), a greater number of years of sexual activity and contact with female sex workers), studies looking at the prevalence and incidence of these infections in the general population and also in populations at increased risk for HIV acquisition, studies showing that HSV-2 is acquired before HIV and finally that individuals with pre-existing HSV-2 are more likely to acquire HIV and that the prevalence of HSV-2 infection in the general population has a major impact on the sexual transmission of HIV. Cohort and nested case-control studies provided information about pre-existing HSV-2 and HIV acquisition and the relative risk (RR) ratio was 2.1 (95% confidence interval, 1.4-3.2). By using this estimate, it has been calculated that in HSV-2-positive individuals, 52% of sexually transmitted risk can be attributed to HSV-2. In addition, the calculated population-attributable risk percentage (also know as the aetiological fraction) varied with the HSV-2 seroprevalence in the population. In populations where HSV-2 prevalence is 80% or more, almost half of the sexually acquired HIV can be attributed to HSV-2.