become infected, we can expect to observe more female-to-male transmission regardless of its efficiency. Pre¬ vention programs are necessary to control spread within these areas and to stem further epidemic spread to other areas and populations. women
Nancy S. Padian, PhD Stephen C. Shiboski, PhD University of California, San Francisco Nicholas P. Jewell, PhD University of California, Berkeley 1. Winkelstein W, Lyman D, Padian N, et al. Sexual practices and risk of infection by the human immunodeficiency virus: the San Francisco Men's Health Study. JAMA. 1987;257:321-325. 2. Anderson RR, May RR, Boily MC, et al. The spread of HIV-1 in Africa: sexual contact patterns and the predicted demographic impact of AIDS. Nature. 1991;352:581-589.
The following reply.— .
letter
was
received
after the authors had
mitten their
To the Editor.\p=m-\In a partner study on HIV transmission among heterosexual couples, Padian et al1 observed only one case (1.4%) of male-to-female transmission of HIV in their study of 72 male partners of HIV-infected women. The observed case was in a couple described as unique in that vag-
inal and penile bleeding during intercourse was noted. However, since nearly half (32/72) of the couples studied used condoms, the risk of transmission may have been underestimated. On the other hand, male-to-female transmission was estimated to be 17.5 times more effective than female-to-male transmission (crude OR). Apart from the fact that the 90% CI for the OR given in the article is large (3.5 to 353), and the usual 95% CI would be still larger, the crude measurement of the relative efficiency of HIV transmission in both directions may be invalid for at least one reason: the authors did not take into account the clinical status of the index case (defined as the potentially infectious member of the couple), which has been found to be associated with a higher proba¬ bility of partner infection in almost all partner studies.2 Fur¬ thermore, female index cases were significantly less often symptomatic than male index cases in the study by Padian et al and thus had probably been infected for shorter periods. Therefore, male-to-female and female-to-male transmission are hardly comparable with these data. In the Multicentric European Partner Study,3 19 cases of female-to-male transmission were observed among 159 cou¬ ples (12%) compared with 82 of 404 cases (20%) of male-tofemale transmission (crude OR 1.9 [95% CI, 1.1 to 3.3]). Furthermore, men having unprotected sexual contacts with women presenting with clinical or biologic signs of immu¬ nodeficiency were found to be infected more often than women having unprotected sex with asymptomatic HIV-infected men =
(42%
vs
15%; P
Nancy S. Padian, PhD Stephen C. Shiboski, PhD University of California, San Francisco Nicholas P. Jewell, PhD University of California, Berkeley 1. Winkelstein W, Lyman D, Padian N, et al. Sexual practices and risk of infection by the human immunodeficiency virus: the San Francisco Men's Health Study. JAMA. 1987;257:321-325. 2. Anderson RR, May RR, Boily MC, et al. The spread of HIV-1 in Africa: sexual contact patterns and the predicted demographic impact of AIDS. Nature. 1991;352:581-589.
The following reply.— .
letter
was
received
after the authors had
mitten their
To the Editor.\p=m-\In a partner study on HIV transmission among heterosexual couples, Padian et al1 observed only one case (1.4%) of male-to-female transmission of HIV in their study of 72 male partners of HIV-infected women. The observed case was in a couple described as unique in that vag-
inal and penile bleeding during intercourse was noted. However, since nearly half (32/72) of the couples studied used condoms, the risk of transmission may have been underestimated. On the other hand, male-to-female transmission was estimated to be 17.5 times more effective than female-to-male transmission (crude OR). Apart from the fact that the 90% CI for the OR given in the article is large (3.5 to 353), and the usual 95% CI would be still larger, the crude measurement of the relative efficiency of HIV transmission in both directions may be invalid for at least one reason: the authors did not take into account the clinical status of the index case (defined as the potentially infectious member of the couple), which has been found to be associated with a higher proba¬ bility of partner infection in almost all partner studies.2 Fur¬ thermore, female index cases were significantly less often symptomatic than male index cases in the study by Padian et al and thus had probably been infected for shorter periods. Therefore, male-to-female and female-to-male transmission are hardly comparable with these data. In the Multicentric European Partner Study,3 19 cases of female-to-male transmission were observed among 159 cou¬ ples (12%) compared with 82 of 404 cases (20%) of male-tofemale transmission (crude OR 1.9 [95% CI, 1.1 to 3.3]). Furthermore, men having unprotected sexual contacts with women presenting with clinical or biologic signs of immu¬ nodeficiency were found to be infected more often than women having unprotected sex with asymptomatic HIV-infected men =
(42%
vs
15%; P
