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Colorado Springs, Colorado
Baeten et al. rigorously analyze data they prospectively collected, during a 4-year interval, from 795 Kenyan men in the trucking industry [1]. Given the available information, they leave no stones unturned, yet potential threats to the validity of their estimates of female-to-male HIV-1 transmission efficiency linger because of uncertainties regarding the precision of their data. On the basis of detail furnished in their Subjects and Methods section, I'm left with the uncomfortable feeling that the authors made default assumptions about the sex of their Kenyan subjects' partners and about the sex acts themselves. I'm concerned with the reported lack of specificity in asking the truckers, during their quarterly follow-up interview, about "the number of sex acts with each of 3 different partner types (wives, casual partners, and prostitutes)" (p. 547). How were these questions phrased (e.g., was the sex of "casual partners" assumed to be female were "sex acts" assumed to be penile-vaginal) and how were these data captured (paper questionnaire face-to-face interview computer assisted) Could misinterpretation of ambiguous questions by respondents have contributed to "confounding by behavioral practices" (p. 551), which the authors tried hard to avoid
Of additional concern is the lack of control for confounding parenteral exposure. HIV-1 is not a sexually transmitted but a sexually transmissible infection; there are ways other than sex to transmit the virus, a consideration of special concern in countries where use of contaminated sharps in medical, dental, and ritualistic settings is common [2]. In addition, the authors provide no information that associates HIV-1 seroconversion with histories of genital symptoms or with receiving medical care for such symptoms. It is possible, for example, that uncircumcised men were more likely to acquire genital infection than were their circumcised counterparts and, perhaps, to have been treated at a facility with injection equipment contaminated with HIV-1.
That default assumptions should be avoided is emphasized by a recent study indicating that bisexuality and anal intercourse may be common in sub-Saharan Africa and that, because of strong taboos against homosexuality, men may be reluctant to reveal such exposures [3]. Of immediate relevance are reports of homosexual sex between Kenyan truck drivers and teenage boys [4]; did the authors probe for such liaisons, or did they avoid asking about them, knowing that homosexuality is illegal in Kenya Finally, the authors report "the probability of female-to-male HIV-1 transmission for a single act of penile-vaginal intercourse...to be 0.0063" (p. 548). It is not clear from their Subjects and Methods section how they knew that the sex act was penile-vaginal. This is possibly important in light of a recent study showing that 14% of prostitutes in a Kenyan sample admitted to having anal intercourse [5]. Were data on anal exposures sought
Considering the substantial reported anomalies in the "heterosexual transmission" view of HIV dynamics in sub-Saharan Africa [6] and reports of data-based estimates that much transmission may be due to undersuspected and underevaluated parenteral exposures [7, 8], care must be taken to ask precise questions and to control for confounding variables, especially in poor countries where parenteral exposure may play a larger role in HIV-1 transmission than heretofore believed. Failure to address such potential threats to validity undermines the credibility of the "female-to-male" or "penile-vaginal" HIV-1 transmission efficiency estimates for circumcised and uncircumcised men that the authors present. Finally, mathematical models using potentially invalid estimates should be evaluated with appropriate circumspection.
References
1. Baeten JM, Richardson BA, Lavreys L, et al. Female-to-male infectivity of HIV-1 among circumcised and uncircumcised Kenyan men. J Infect Dis 2005; 191:54653. First citation in article
2. Simonsen L, Kane A, Lloyd J, Zaffran M, Kane M. Unsafe injections in the developing world and transmission of bloodborne pathogens: a review. Bull WHO 1999; 77:789800. First citation in article
3. Brody S, Potterat JJ. Assessing the role of anal intercourse in the epidemiology of AIDS in Africa. Int J STD AIDS 2003; 14:4316. First citation in article
4. HIV and Kenya's homosexuals. Afr Health 1998; 20:48. First citation in article
5. Fonck K, Kaul R, Kimani J, et al. A randomized, placebo-controlled trial of a monthly azithromycin prophylaxis to prevent sexually transmitted infections and HIV-1 in Kenyan sex workers: study design and baseline findings. Int J STD AIDS 2000; 11:80411. First citation in article
6. Brewer DD, Brody S, Drucker E, et al. Mounting anomalies in the epidemiology of AIDS in Africa: cry the beloved paradigm. Int J STD AIDS 2003; 14:1447. First citation in article
7. Gisselquist D, Rothenberg R, Potterat J, Drucker E. HIV infections in sub-Saharan Africa not explained by sexual or vertical transmission. Int J STD AIDS 2002; 13:65766. First citation in article
8. Gisselquist D, Potterat JJ. Heterosexual transmission of HIV in Africa: an empiric estimate. Int J STD AIDS 2003; 14:16273. First citation in article