London School of Hygiene & Tropical Medicine

HIV contaminated injections are unlikely to account for a large proportion of HIV incidence in sub-Saharan Africa, according to a new study, the results of which are published today in Proceedings of the National Academy of Sciences, USA.

There is a lack of data relating to the risk of HIV transmission from contaminated injections, and this has made it difficult to assess their impact on HIV transmission in the region. Previous estimates have varied widely, ranging from 2.5% to more than 30%.

There have been suggestions that HIV-contaminated injections might be a major, but largely overlooked, route of HIV transmission in sub-Saharan Africa. If true, this would have profound implications for HIV control policy in the region. A team led by researchers from the London School of Hygiene & Tropical Medicine sought to determine a means of more accurately quantifying the likely proportion of HIV incidence due to injections contaminated with HIV.

The team has developed an age-stratified model that accounts for transmission due to unsafe injections, unsafe transfusions, and mother-to-child transmission. They applied it using data from a cohort study in southwest Uganda, observational studies within East Africa, and a systematic literature review and meta-analysis.

They found that, in rural Uganda, the most plausible estimates of the proportion of HIV incidence due to contaminated injections were 0-6%. Higher estimates were less consistent with the data on observed HIV incidence. Over all ages, more than half the HIV incidence was left unexplained by unsafe injections, unsafe transfusions and mother-to-child transmission. Sexual transmission was the most credible explanation for this unexplained incidence in adults.

Richard G White, Lecturer in Infectious Disease Modelling at the London School of Hygiene & Tropical Medicine and lead author of the study, comments: 'The findings are likely to apply to other populations in sub-Saharan Africa because they were primarily determined by the low rates of HIV infection among 5-12 year olds relative to other age groups, an observation common to many other populations in sub-Saharan Africa. Indeed, any claim that transmission from unsafe injections represents a large proportion of overall HIV incidence must provide a plausible explanation for how this age group escapes infection'.