Heterosexual Infectivity of HIV Underestimated
NEW YORK (Reuters Health) Aug 05 - The heterosexual infectivity of HIV-1 is commonly cited as a fixed value of approximately one transmission per 1000 sexual contacts. However, depending on the presence of several risk factors, the rate of transmission may be several hundred times higher, according to research presented Monday at the International AIDS Conference in Mexico City and published online on August 5 by The Lancet Infectious Diseases.
“Claims in both the popular media and the peer-reviewed literature that HIV is very difficult to transmit heterosexually are dangerous in any context where the possibility of HIV exposure exists,” the researchers at the University of North Carolina in Chapel Hill maintain in their paper.
Dr. Myron S. Cohen and his colleagues examined heterosexual HIV infectivity cofactor effects in a systematic literature review and meta-analysis that included 27 articles that reported on 15 unique study populations.
Infectivity estimates ranged from approximately zero among susceptible men without genital ulcer disease, most of whom were circumcised, to one transmission event for every 3.1 contacts for penile-anal sex between late-stage male index cases and susceptible women, about half of whom had a sexually transmitted infection (STI).
In meta-regression analysis, the cofactors most strongly associated with infectivity were genital ulcer disease in susceptible individuals, lack of circumcision in susceptible men, and early-stage or late-stage infection in index cases vs mid-stage infection. These cofactors each increased the risk of infection by 2 to 8 transmissions per 1000 sexual contacts.
Limited data also suggested that infectivity is higher for penile-anal vs penile-vaginal sex, for susceptible individuals with vs without STI, and for older vs younger index cases.
However, infectivity was only weakly associated with direction of transmission and mean susceptible age.
Dr. Cohen’s team notes that their review did not take into account increased transmission during the acute, pre-seroconversion phase of infection and other periods of high viral load, or the effects of antiretroviral treatment, condom-protected acts, or additional sexual partners.
This review, the authors conclude, “highlights the need for further infectivity research, and reinforces the importance of including cofactor effects in HIV epidemic models, policy considerations, and prevention messages.”
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