In this issue (see page 411), Kalichman et al1 report the results of a cross-sectional study on anal intercourse (AI) of heterosexual men and women in South Africa (SA).1 This study is a welcome addition to the literature, since there are relatively few studies quantifying rates of AI among heterosexual populations, especially in SA. Overall, 14% men and 10% women reported AI in the previous 3 months. Among those, 56% did in at least 50% of all sex acts and reported using condoms as often for AI as for vaginal intercourse (VI). Despite this, the authors concluded that the rate of AI was relatively low among heterosexuals and that, “even among those who do engage in AI, most do so at significantly lower rates than VI” (total VI = 9.90, total AI = 8.47) based on reported mean frequencies of all (protected and unprotected) VI and AI (table 3)*. However, we believe that the observed differences in unprotected VI and AI are not sufficient to assert this with confidence, especially for men (mean frequency of unprotected AI and VI acts: 3.61 and 4.56 respectively for females, 3.11 and 3.04 for males). They further argued that, although the role of AI remains unclear, the HIV epidemic in SA cannot be primarily attributed to AI and that AI “should neither be the focus of nor ignored by HIV prevention interventions in SA.” They also suggest that, relative to VI, AI is unlikely to account for a large fraction of new HIV infections in Africa, but its role should not be underestimated given its higher transmission efficiency.

As stated by the authors, an important limitation of these results is that the AI rate may be underestimated, given the sensitivity of subject matter and the interviewing method used (self-administered questionnaire with minimal assistance). Studies …