People with pre-existing human papillomavirus (HPV) infection have a higher risk of contracting HIV than their uninfected peers, according to a systematic review and meta-analysis.
The findings bolster several recent sub-analyses of cohort data from sub-Saharan Africa, which have pointed to a link between the two infections.
This was "particularly interesting," Dr Catherine Houlihan told Reuters Health, "because HPV is one of the commonest sexually transmitted infections across the world, and it is possible to prevent infection with some types of HPV using a currently available vaccine. It was therefore important to critically review the published studies, and consider combining the data." She and her colleagues did just that, and their findings were published online in the journal Aids.
They included eight published studies in their analysis, along with other unpublished data from five of the authors. They analysed the findings in three separate groups; women, heterosexual men, and men who have sex with men.
Additional data obtained
"We also obtained additional data from the authors on associations with specific HPV genotypes, in particular those covered by the vaccines," Dr Houlihan, from the London School of Hygiene and Tropical Medicine in the UK, told Reuters Health. "Our analyses were restricted to longitudinal studies, so that we could disentangle the time order of HPV infection and HIV infection." Seven of the studies found an association between prevalent HPV and HIV acquisition, the authors report.
Six of the studies looked at women, and all of these were from Africa. In these studies, the risk of HIV acquisition rose significantly with prevalent HPV infection with any genotype (hazard ratio, 2.06), although adjustment for confounding factors was often "inadequate," the authors note.
The association was similar for both high-risk and low-risk HPV types (HR, 1.99 and 2.01, respectively), with weak evidence of publication bias. Unpublished data from one of two studies in women indicated an association between genotypes targeted by HPV vaccines and HIV acquisition, the investigators note.
"In the two studies in men, a similar increase in the risk of acquiring HIV was seen," Dr Houlihan said, "(but) the associations with vaccine types were not consistent." According to the researchers, the calculated population-attributable fractions of HIV cases due to infection with any HPV type ranged from 21% to 37%. They say more study is needed to assess whether HPV vaccination might have an effect on HIV incidence.
HPV increases risk for infection
"The studies in women," Dr Houlihan said, "suggest with reasonable consistency that, in populations with high incidence of HIV, being infected with HPV may increase the risk of becoming HIV positive. However, there are over 40 genotypes of HPV that infect the human genital tract, and current HPV vaccines only directly cover four of those genotypes. There are currently insufficient data on associations with vaccine types to allow reliable estimates of the potential impact of HPV vaccination on HIV incidence."
Dr Houlihan emphasised that current vaccines "are important in the prevention of cervical cancer and should continue to be promoted as such. More evidence is needed to evaluate their potential role in modifying HIV risk."
The studies had their share of problems, Dr Houlihan said. For example, "important confounders such as sexual behaviour and some sexually transmitted diseases were not always accounted for. None of the studies were designed or powered to detect HPV as a risk factor for HIV, and most of them were in populations at high risk of HIV, such as sex workers."
(Reuters Health, Megan Brooks, September 2012)
Symptoms and phrases of HIV
Who should get the HPV vaccine