Evidence before this study
infections
INFECTION TOE, INFECTIONS
We searched PubMed, with no date or language filters, to identify previous quantitative studies investigating the role of age, sex, mobility, and drug resistance mutations (separately or in combination) as drivers of new heterosexual HIV transmissions in sub-Saharan Africa. Observational studies were considered along with those using phylogenetic or mathematical modelling methodologies.In observational studies, having an older partner or a migrant partner is frequently identified as a risk factor for HIV acquisition, particularly in women, but this is a slightly separate question to the quantification of the overall frequency of these demographics among the sources of new infections. The most recent studies of drug resistance have shown an increasing prevalence, particularly in non-nucleoside reverse transcriptase inhibitor resistance.The ability to use phylogenetics to investigate HIV transmission is reasonably recent, and the ability to use it to reconstruct who infected whom in transmission pairs is more recent still. One previous, influential study in South Africa posited a key role of men in their 30s in infecting very young women, and being themselves infected by women in their 30s, but that work did not use a methodology that was able to accurately reconstruct direction of transmission. A more recent study in Botswana found similar age distributions for male and female sources of transmission, with the average individual being in their late 30s or early 40s. However, these ages were recorded at the time of study enrolment and do not take into account the time from infection to sampling. The paper also showed that, in that setting, the majority of transmissions were between members of the same community. A number of other phylogenetic studies have been concerned with the very specific dynamics of HIV-1 in the fishing communities of Lake Victoria. No previous phylogenetics work to our knowledge has considered the distribution of drug resistance mutations in sources, and none considered the interaction between source characteristics.We were unable to find any previous mathematical modelling studies for which the characterisation of sources according to these variables was a major focus.