CAPE TOWN, SOUTH AFRICA Men who tested positive for human papillomavirus had an 80% increase in the risk of contracting HIV, based on an analysis of data collected during the Kisumu, Kenya, trial that examined the role of male circumcision in HIV risk.
That study showed that circumcision reduced the risk of getting HIV by more than 50%, Jennifer S. Smith, Ph.D., noted at the fifth International AIDS Society conference on pathogenesis, treatment, and prevention of HIV.
As an additional component of the study, researchers collected data on other sexually transmitted diseases, including HPV, she said in a late-breaker session. Samples were taken from the penile shaft and foreskin, and from the glans and coronal sulcus.
"Many [sexually transmitted infections] have been previously found to be associated with increased risk of HIV infection. However, surprisingly few data are available currently on any potential effect of HPV on HIV acquisition risk," said Dr. Smith of the University of North Carolina, Chapel Hill.
The researchers compared the 42-month risk of HIV seroconversion among 2,168 men, 1,089 of whom were positive for HPV at the start of the study. High-risk HPV strains, those associated with cancers, were present in 754 men and low-risk strains were seen in 335.
The researchers controlled for the effect of circumcision, the main intervention in the study. They found that the risk for HIV was increased only when positive HPV samples were obtained from the glans. The risk of contracting HIV over the study period was 5.8% in those with positive samples from the glans and 3.7% for men with negative samples from the glans at baseline. The difference was significant at P = .01.
The acquisition rates translated into a hazard ratio of 1.8, with a 95% confidence interval from 1.1 to 2.9, Dr. Smith said. The risk of contracting HIV was not influenced by the type of HPV isolated.
Dr. Smith said possible explanations for the increased risk include residual confounding because of sexual behavior, or some sort of biological mechanism. The virus might induce local cytokines, such as macrophage inflammatory protein-3 and interleukin-8 that could play a role in susceptibility to HIV infection.
The immunological process of clearing an HPV infection also might bring increased numbers of CD4-positive T cells, the targets of HIV, to sites where they could be infected, she said.
Further, the association might simply be "a marker for [risky] sexual behavior," said Timothy Farley, Ph.D., of the World Health Organization's reproductive health department. Dr. Farley chaired the session at which the research was presented. The process of clearing the papillomaviruswhich can occur repeatedlymay have some immunological consequences that increase susceptibility to HIV.
"It's speculation as to what the mechanism might be, but it's an intriguing one," he said.
Whether a vaccine approach might affect the risk is also up in the air, he said, noting that current vaccines target the high-risk, cancer-causing strains of HPV, while Dr. Smith's study showed no difference in HIV risk based on the HPV strain involved.
Dr. Farley noted that another circumcision trial, conducted in South Africa, had also shown an increased HIV risk for men infected with HPV.
The Kisumu study was supported by the National Institute of Allergy and Infectious Diseases. Dr. Smith did not report any conflicts of interest.