Heterosexual HIV Infectivity Rate May Be Underestimated

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Title: Heterosexual HIV Infectivity Rate May Be Underestimated
URL: http://www.pslgroup.com/dg/227696.htm
Doctor's Guide
August 7, 2008

NEW YORK -- August 7, 2008 -- The heterosexual infectivity rate of HIV is generally underestimated because it does not take into account risk factors that can multiply the chances of transmission by a factor of several times to several hundred times, according to a study in the September issue of The Lancet Infectious Diseases.

The article is published early online, and the findings are being announced at the 17th International AIDS Conference, Mexico City, Mexico.

Kimberly Powers, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, and colleagues reviewed published data on HIV up to April 2008 in order to estimate the effects of so-called transmission cofactors.

Their results were extremely varied, with estimates ranging from 0 transmissions after more than 100 penile-vaginal contacts in some serodiscordant couples, to 1 transmission for every 3.1 episodes of heterosexual anal intercourse -- more than 300 times the fixed heterosexual infectivity rate commonly quoted.

Infectivity differences, expressed as the number of transmissions per 1,000 contacts, were 8.1 comparing uncircumcised to circumcised susceptible men (13.2 vs 5.1 infections per 1,000 contacts), 6.0 comparing susceptible individuals with and without genital ulcer disease (7.5 vs 1.5), 1.9 comparing late- to mid-stage index cases (2.6 vs 0.7), and 2.5 comparing early- to mid-stage index cases (3.2 vs 0.7).

"The use of a single, 'one-size-fits-all' value for the heterosexual infectivity of HIV-1 obscures important differences associated with transmission cofactors. Perhaps, more important, the particular value of 0.001 that is commonly used seems to represent a lower bound," the authors wrote.

"As such, this value substantially underestimates the infectivity of HIV-1 in many heterosexual contexts," the authors wrote. "Heterosexual infectivity can exceed 0.1 for penile-vaginal contact or even 0.3 for penile-anal contact. 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.

"Improved infectivity estimates, especially more detailed estimates that quantify the amplifying effects of biological cofactors, will help us to grasp the magnitude of the HIV epidemic, to accurately communicate the level of risk involved in heterosexual sex, and to identify the best possible intervention strategies for slowing the epidemic's spread," the authors wrote.

"Infectivity studies are very difficult to conduct, and few studies exist as a result. Many of the studies producing the published estimates suffered from at least 1 potential bias. Therefore, while our study documents the considerable heterogeneity of the heterosexual infectivity of HIV-1 and provides some explanations for this heterogeneity, considerable uncertainty remains."

SOURCE: The Lancet Infectious Diseases

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