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An epidemiological analysis in the March issue of Sexually Transmitted Diseases casts doubt on a controversial theory that most cases of HIV in sub-Saharan Africa are transmitted by medical injections performed with re-used needles, rather than by sexual contact.
Led by Katherine French, PhD, of ImperialCollege in London, the researchers developed mathematical models simulating the two routes of HIV spread. The models tested various assumptions regarding how many unsafe injections and what rates of HIV transmission would be needed to create an HIV epidemic over a 22-year period.
The results did not support the iatrogenic theory of transmission by unsafe medical injections. The numbers of unsafe injections and the probabilities of HIV transmission needed to reach the prevalence rates of HIV infection observed in sub-Saharan African nations were "unfeasibly high," French and her coauthors write.
For example, assuming an average of two unsafe injections per year, the transmission risk would have to be about 40 percent to result in an HIV epidemic affecting 7.5 to 25 percent of the adult population. In contrast, real-world studies suggest that the risk of becoming infected with HIV from a contaminated needle is less than three percent.
Other scenarios were tested, but also seemed inconsistent with the rates of HIV infection observed in Africa. The prevalence of HIV infection in sub-Saharan African nations ranges from one to 37 percent.
In contrast, the assumptions necessary to produce an HIV epidemic through sexual transmission were well within the bounds of plausibility. The most important factor was the number of different sexual partnerseven small changes in the "partner change rate" had a major impact on the rate of HIV transmission.
Since 2002, a series of articles by a small group of scientists has questioned the assumption that heterosexual intercourse is the main mode of HIV transmission in sub-Saharan Africa. Instead, these researchers have argued that unsafe medical injections are the major cause. They cite research showing that HIV infection is more strongly linked with the number of medical injections received than with sexual behavior among adults in sub-Saharan African nations.
Even simple "back-of-the-envelope" calculations show the difficulty of explaining HIV epidemic spread on the basis of unsafe injections, according to Drs. Richard J. Hayes and Richard G. White of the London School of Hygiene and Tropical Medicine, authors of an editorial accompanying the new study. They write, "[Heterosexual transmission is able to explain epidemics compatible with those seen in Africa for a range of assumptions lying well within plausible bonds." The success of HIV-prevention programs targeting sexual behavior in Uganda further back the theory of sexual transmission.
The new analysis has several limitationsnotably including the fact that it focused on adults rather than children, who receive a higher frequency of medical injections. While it is true that unsafe injections with re-used needles could be responsible for some cases, they are unlikely to be the main source of HIV spread in sub-Saharan Africa. Hayes and White conclude, "Although control programs in such countries must ensure that iatrogenic transmission is reduced to a minimum, greater reductions in HIV spread will be achieved through more vigorous measures to promote safer behavior, which need political leadership at the highest levels.
Source: Lippincott Williams & WilkinsÂ Â Â Â