The scientific evidence for HIV/AIDS

HIV heterosexual transmission and the "Padian paper myth"

One of the more egregious myths perpetrated by AIDS denialists is that HIV is not heterosexually transmitted. Part of the "evidence" that underlies this myth is a 1997 paper by Dr. Nancy Padian and her colleagues at the University of California, San Francisco

(Padian NS, Shiboski SC, Glass SO, Vittinghoff E. 1997. Heterosexual transmission of human immunodeficiency virus (HIV) in Northern California: results from a ten-year study. Am J Epidemiol 146, 350-357) (1). The denialists either misinterpret or misunderstand this paper. Some internet sites/Blogs even go so far as to suggest that the "HIV/AIDS establishment" (sic) finds Dr. Padian's work inconvenient and has suppressed it, to the detriment of her professional career. The following commentary from Dr. Padian addresses HIV heterosexual transmission, discusses what her seminal 1997 paper does actually say and, ipso facto, speaks to the absurdity of the notion that her work has been suppressed, or is inconvenient to other AIDS researchers.

Heterosexual transmission of HIV – Nancy Padian, PhD

HIV is unquestionably transmitted through heterosexual intercourse. Indeed, heterosexual intercourse is now responsible for 70-80% of all HIV transmissions worldwide (2). The current likelihood of male to female infection after a single exposure to HIV is 0.01-0.32% (2, 3), and the current likelihood of female to male infection after a single exposure is 0.01-0.1% (2). These estimates are mostly derived from studies in the developed world. However, a man or a woman can become HIV-positive after just one sexual contact. In developing countries, particularly those in sub-Saharan Africa, several factors (co-infection with other sexually transmitted diseases, circumcision practices, poor acceptance of condoms, patterns of sexual partner selection, locally circulating viral subtypes, high viral loads among those who are infected, etc.) can increase the likelihood of heterosexual transmission to 20% or even higher (4). Evidence that specifically documents the heterosexual transmission of HIV comes from studies of HIV-discordant couples (i.e., couples in a stable, monogamous relationship where one partner is infected and the other is not); over time, HIV transmission occurs (5). Other studies have traced the transmission of HIV through networks of sexual partners (6-9). Additional evidence comes from intervention studies that, for example, promote condom use or encourage reductions in the numbers of sexual partners: the documented success of these interventions is because they prevent the sexual transmission of HIV (1,10,11).

In short, the evidence for the sexual transmission of HIV is well documented, conclusive, and based on the standard, uncontroversial methods and practices of medical science. Individuals who cite the 1997 Padian et al. publication (1) or data from other studies by our research group in an attempt to substantiate the myth that HIV is not transmitted sexually are ill informed, at best. Their misuse of these results is misleading, irresponsible, and potentially injurious to the public.

A common practice is to quote out of context a sentence from the Abstract of the 1997 paper: "Infectivity for HIV through heterosexual transmission is low". Anyone who takes the trouble to read and understand the paper should appreciate that it reports on a study of behavioural interventions such as those mentioned above: Specifically, discordant couples were strongly counseled to use condoms and practice safe sex (1,12). That we witnessed no HIV transmissions after the intervention documents the success of the interventions in preventing the sexual transmission of HIV. The sentence in the Abstract reflects this success – nothing more, nothing less. Any attempt to refer to this or other of our publications and studies to bolster the fallacy that HIV is not transmitted heterosexually or homosexually is a gross misrepresentation of the facts and a travesty of the research that I have been involved in for more than a decade.

If safe sex practices are followed, and if there are no complicating factors such as those mentioned above, the risk of HIV transmission can be as low as our studies suggestÖIF. But many people misunderstand probability: they think that if the chance of misfortune is one in six, that they can take five chances without the likelihood of injury. This "Russian Roulette" misapprehension is dangerous to themselves and to others. Furthermore, complicating factors are often not evident or obvious in a relationship, so their perceived absence should not be counted on as an excuse not to practice safe sex.

Finally, it is a complete fallacy to allege or insinuate that this work has been "suppressed" or "ignored" by the AIDS community or
unsupported by UCSF or any other institution with which I have worked. To the contrary, these findings have been seen as central and seminal
to the problem of heterosexual transmission rates and the development of interventions to lower the rate of transmission and infection worldwide,
many of which are being conducted by my research group. The success of my working group has been fueled, not hindered, by our research on the
heterosexual transmission of HIV, attested to by our long record of peer-reviewed publications.

Nancy Padian is a Professor of Obstetrics, Gynecology and Reproductive Sciences at the University of California and she has worked on the heterosexual transmission of HIV since 1984. She is a frequent participant in annual NIH Office of AIDS Research planning workshops and has chaired the workshop on international research for the last four years. She is an elected member to the Institute of Medicine and the American Epidemiology Society. She served as vice-chair of the University of California task force on AIDS and currently directs international research for UCSF Global Health Sciences, the UCSF AIDS Research Institute and she is co-director of the Center for Reproductive Health Research and Policy.

  1. Padian NS, Shiboski SC, Glass SO, Vittinghoff E. Heterosexual transmission of human immunodeficiency virus (HIV) in Northern California: results from a ten-year study. Am J Epidemiol 1997;146:350-7.


  2. Downs AM, De Vincenzi I. Probability of heterosexual transmission of HIV: relationship to the number of unprotected sexual contacts. European Study Group in Heterosexual Transmission of HIV. J Acquir Immune Defic Syndr Hum Retrovirol. 1996 Apr 1;11(4):388-95.


  3. Wiley JA, Herschhkorn SJ, Padian NS. Heterogeneity in the probability of HIV transmission per sexual contact: the case of male-to-female transmission in penile-vaginal intercourse. Stat Med 1989;8:93-102.


  4. Gray RH, Wawer MJ, Brookmeyer R, Sewankambo NK, Serwadda D, Wabwire-Mangen F, Lutalo T, Li X, vanCott T, Quinn TC; Rakai Project Team. Probability of HIV-1 transmission per coital act in monogamous, heterosexual, HIV-1-discordant couples in Rakai, Uganda. Lancet. 2001 Apr 14;357(9263):1149-53.


  5. Ellerbock TV, Lieb S, Harrington PE, et al. Heterosexually transmitted human immunodeficiency virus infection among pregnant women in a rural Florida community. N Engl J Med 1992;327:1704-9.



  6. Hunter DJ. AIDS in sub-Saharan Africa: the epidemiology of heterosexual transmission and the prospects for prevention. Epidemiology. 1993 Jan;4(1):63-72. Review.


  7. Venkataramana CB, Sarada PV. Extent and speed of spread of HIV infection in India through the commercial sex networks: a perspective. Trop Med Int Health. 2001 Dec;6(12):1040-61.


  8. Adimora AA, Schoenbach VJ, Doherty IA. HIV and African Americans in the southern United States: sexual networks and social context. Sex Transm Dis. 2006 Jul;33(7 Suppl):S39-45.


  9. Latora V, Nyamba A, Simpore J, Sylvette B, Diane S, Sylvere B, Musumeci S. Network of sexual contacts and sexually transmitted HIV infection in Burkina Faso. J Med Virol. 2006 Jun;78(6):724-9.


  10. Ghys PD, Diallo MO, Ettiegne-Traore V, Kale K, Tawil O, Carael M, et al. Increase in condom use and decline in HIV and sexually transmitted diseases among female sex workers in Abidjan, Cote d'Ivoire, 1991-1998. AIDS 2002;16(2):251-58.


  11. Katzenstein DA, McFarland W, Mbizo M, Latif AS, Machekano R, Parsonnet J, et al. Peer education among factory workers in Zimbabwe: providing a sustainable HIV prevention intervention. Paper presented at the 12th International Conference on AIDS, Geneva, June 28-July 3, 1998.


  12. Padian NS, O'Brien TR, Chang Y, Glass S, Francis DP. Prevention of heterosexual transmission of human immunodeficiency virus through couple counseling. J Acquir Immune Defic Syndr. 1993 Sep;6(9):1043-8