An expanding body of evidence challenges the conventional hypothesis that sexual transmission is responsible for more than 90% of adult HIV infections in Africa. Differences in epidemic trajectories across Africa do not correspond to differences in sexual behaviour. Studies among African couples find low rates of heterosexual transmission, as in developed countries. Many studies report HIV infections in African adults with no sexual exposure to HIV and in children with HIV-negative mothers. Unexplained high rates of HIV incidence have been observed in African women during antenatal and postpartum periods. Many studies show 20%–40% of HIV infections in African adults associated with injections (though direction of causation is unknown). These and other findings that challenge the conventional hypothesis point to the possibility that HIV transmission through unsafe medical care may be an important factor in Africa's HIV epidemic. More research is warranted to clarify risks for HIV transmission through health care.

The consensus among influential AIDS experts that heterosexual transmission accounts for 90% of HIV infections in African adults emerged no later than 1988. We examine evidence available through 1988, including risk measures associating HIV with sexual behaviour, health care, and socioeconomic variables, HIV in children, and risks for HIV in prostitutes and STD patients. Evidence permits the interpretation that health care exposures caused more HIV than sexual transmission. In general population studies, crude risk measures associate more than half of HIV infections in adults with health care exposures. Early studies did not resolve questions about direction of causation (between injections and HIV) and confound (between injections and STD). Preconceptions about African sexuality and a desire to maintain public trust in health care may have encouraged discounting of evidence. We urge renewed, evidence-based, investigations into the proportion of African HIV from non-sexual exposures.

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Summary:The transmission ef® ciency of HIV-1 through unsafe medical injections can be estimated from seroconversions among health care workers (HCWs) after percutaneous exposures and documented iatrogenic outbreaks. Data from a case± control study of seroconversion after percutaneous exposures among US and European HCWs shows an average rate of seroconversion after deep injuries Ð arguably comparable to unsafe injections Ð of 2.3%. Information from an iatrogenic HIV outbreak in a Romanian orphanage suggests a transmission ef® ciency of 2± 7%. Even these estimates may be too low to explain the rapid spread of HIV among Russian and Libyan children in iatrogenic outbreaks discovered in 1988 and 1998, respectively. In countries in sub-Saharan Africa and elsewhere with high HIV prevalence and large numbers of unsafe injections, personal risk as well as the share of the HIV epidemic associated with unsafe injections may be an order of magnitude higher that many experts have supposed.

For more than a decade, most experts have assumed that more than 90% of HIV in African adults results from heterosexual transmission. In this exercise, we show how data from studies of risk factors for HIV can be used to estimate the proportion from sexual transmission, and we present our estimates. Calculating two ways from available data, our two point estimates - we do not estimate confidence intervals - are that 25-29% of HIV incidence in African women and 30-35% in men is attributable to sexual transmission; these estimates assume 10% annual epidemic growth. These findings call for reconceptualization of research to more accurately assess routes of HIV transmission.