The recent report by Pettifor and colleagues  clearly illustrates the fundamental weakness of HIV epidemiology in sub-Saharan Africa: its singular focus on sexual risk factors. The narrowness of their investigation is particularly disheartening because they began collecting data after a series of widely discussed articles by Gisselquist and colleagues [2–4] was published. These (admittedly controversial) papers not only presented evidence suggesting a very substantial role for parenteral (puncturing, especially in healthcare settings) transmission of HIV in sub-Saharan Africa, but also highlighted nearly a dozen serious anomalies with the conventional view (that nearly all transmission is caused by penile–vaginal intercourse). An incomplete approach to studying HIV transmission should no longer be tolerated. Epidemiological studies that do not entail a broad inventory of both sexual and puncturing exposures to HIV are scientifically suspect and untrustworthy , especially for the design of evidence-based prevention strategies.
Researchers working in rich countries have invested considerable effort to assess the full range of possible puncturing and blood exposures among injection drug users, but researchers working in poor countries have not attempted to do the same for general populations with a substantial exposure to puncturing. Why have HIV epidemiologists working in poor countries, including Pettifor and colleagues, not measured seemingly obvious puncturing risks? Some risk behaviors that should be measured include using a skin-puncturing instrument that has (or might have) previously been used by another person, receiving injections in healthcare settings where HIV is prevalent in patients, and using (or possibly using) a skin-puncturing instrument that an HIV-positive individual has previously used, among many others . Unasked questions yield no answers.
A close examination of the results reported by Pettifor et al.  provides evidence suggestive of non-sexual modes of HIV transmission, which they did not consider. In their population-based sample of young South Africans, they found that 2.5% of men and 3.8% of women who reported never having had a sexual partner were HIV positive. (Given the authors' monochromatic view of HIV transmission, it is not surprising they ascribe this anomalous finding to misreporting). Respondents who had ever been tested for HIV were more likely to be HIV positive than those who had not; this may point to HIV exposure in healthcare settings (e.g. contaminated venipuncture equipment). Men reported 50% more sexual partners than women, yet women experienced a 222% higher HIV prevalence than men; this may be related to the greater likelihood of women seeking medical care than men. In addition, the authors found a relationship between their respondents’ reported history of genitourinary symptoms and HIV seropositivity. This association could reflect respondents receiving unsafe injections for sexually transmitted disease (STD) treatment, made even more unsafe by a high HIV prevalence in STD patients. Having received treatment in sub-Saharan Africa for STD (usually in the form of injections) is often more of an HIV risk than having STD without having had injections for treatment . Inattention to non-sexual means of transmission condemns the authors (and readers of the journal) to speculation, a deeply unsatisfying explanation.
In-vitro studies have demonstrated that reasonably healthy vaginal and cervical tissue cannot become infected on exposure to HIV, but that rectal tissue can readily become infected [6,7]. It is therefore a serious problem that the authors of the South African serosurvey failed to measure vaginal and anal exposures separately. The obscuring of massive differences in transmission potential between particular sexual behaviors may be the reason why the authors obtained an association between the number of sexual partners and HIV risk, despite the absence of dose-dependency in most other studies [8,9].
Key modes of HIV transmission have been poorly specified in sub-Saharan Africa long enough. The report by Pettifor et al.  should serve as a painful wake-up call for researchers to return to epidemiological fundamentals: rigorous investigation of the many possible routes of HIV transmission, with an especial emphasis on contact tracing of incident cases and DNA sequencing of cases’ HIV variants [5,10].
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