The Authors reply

Abstract

In their letter, Potterat et al raise the question of whether the high prevalence of HIV observed among young people in South Africa is the result of parenteral HIV exposure. Although we found that young people in South Africa did not report more sexual risk behaviors than their U.S. peers, current evidence suggests that the vast majority of infections in sub-Saharan Africa, including South Africa, are the result of sexual transmission [1Pettifor A.E. Levandowski B.A. Macphail C. et al.A tale of two countries: Rethinking sexual risk for HIV among young people in South Africa and the United States.J Adolesc Health. 2011; 49: 237-243Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar, 2Joint United Nations Programme on HIV/AIDS (UNAIDS)UNAIDS report on the global AIDS epidemic 2010. UNAIDS, Geneva, Switzerland2010Google Scholar]. Several studies have documented that unclean needles contribute only a small proportion of new HIV infections in sub-Saharan Africa [3Thoma M. Gray R.H. Kiwanuka N. et al.Unsafe injections and transmission of HIV-1 in sub-Saharan Africa.Lancet. 2004; 363: 1650-1651Abstract Full Text Full Text PDF PubMed Scopus (7) Google Scholar, 4Schmid G.P. Buvé A. Mugyenyi P. et al.Transmission of HIV-1 infection in sub-Saharan Africa and effect of elimination of unsafe injections.Lancet. 2004; 363: 482-488Abstract Full Text Full Text PDF PubMed Scopus (121) Google Scholar, 5White R.G. Ben S.C. Kedhar A. et al.Quantifying HIV-1 transmission due to contaminated injections.Proc Natl Acad Sci USA. 2007; 104: 9794-9799Crossref PubMed Scopus (24) Google Scholar, 6Walker P.R. Worobey M. Rambaut A. et al.Epidemiology: Sexual transmission of HIV in Africa.Nature. 2003; 422: 679Crossref PubMed Scopus (41) Google Scholar, 7French K. Riley S. Garnett G. Simulations of the HIV epidemic in sub-Saharan Africa: Sexual transmission versus transmission through unsafe medical injections.Sex Transm Dis. 2006; 33: 127-134Crossref PubMed Scopus (17) Google Scholar]. Although measuring all exposures is important when trying to determine the etiology of infection, in a setting such as South Africa, the dominant modifiable risk factor for HIV is sexual behavior. Measuring sexual behavior well is important to understanding transmission and for developing interventions. We do not believe that the combination of high HIV prevalence and the lack of high-risk behavior among South African youth means that they are being significantly exposed through routes other than sexual intercourse. Rather, we hypothesize that a combination of sexual mixing in a high-prevalence setting, structural factors that put young people at increased risk of exposure and unique biological factors, such as the predominance of clade C HIV [8Novitsky V. Ndung'u T. Wang R. et al.Extended high viremics: A substantial fraction of individuals maintain high plasma viral RNA levels after acute HIV-1 subtype C infection.AIDS Lond Engl. 2011; 25: 1515-1522Crossref PubMed Scopus (56) Google Scholar, 9Cohen M.S. Eron J. Soderberg Jr., K. McMichael A. High clade C HIV-1 viremia: How did we get here and where are we going?.AIDS Lond Engl. 2011; 25: 1543-1545Crossref PubMed Scopus (3) Google Scholar], is driving the epidemic in sub-Saharan Africa over and above individual sexual behaviors. Kenyon et al assert that we dismiss the role of behavior, in particular concurrency, and also race in explaining differences in the epidemics observed in South Africa and the United States. The debate on the role of concurrency as a driver of the HIV epidemic in sub-Saharan Africa continues [10Morris M. Kurth A.E. Hamilton D.T. et al.Concurrent partnerships and HIV prevalence disparities by race: Linking science and public health practice.Am J Public Health. 2009; 99: 1023-1031Crossref PubMed Scopus (236) Google Scholar, 11Lurie M.N. Rosenthal S. The concurrency hypothesis in sub-Saharan Africa: Convincing empirical evidence is still lacking Response to Mah and Halperin, Epstein, and Morris.AIDS Behav. 2010; 14: 34Crossref PubMed Scopus (40) Google Scholar, 12Epstein H. Morris M. Concurrent partnerships and HIV: An inconvenient truth.J Int AIDS Soc. 2011; 14: 13Crossref PubMed Scopus (80) Google Scholar, 13Padian N.S. Manian S. The concurrency debate: Time to put it to rest.Lancet. 2011; 378: 203-204Abstract Full Text Full Text PDF PubMed Scopus (24) Google Scholar, 14Tanser F. Barnighausen T. Hund L. et al.Effect of concurrent sexual partnerships on rate of new HIV infections in a high-prevalence, rural South African population: A cohort study.Lancet. 2011; 378: 247-255Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar]. We believe it plays a role and is likely one of several factors contributing to the on-going epidemic. In our South African youth survey, we found that close to 25% of men and 5% of women reported concurrent partners in the past 12 months [[15]Steffenson A.E. Pettifor A.E. Seage III, G.R. et al.Concurrent sexual partnerships and human immunodeficiency virus risk among South African youth.Sex Transm Dis. 2011; 38: 459-466PubMed Google Scholar]. We found it to be associated with HIV infection among women but not men. The question of whether South African young people practice concurrency more than their U.S. peers is unclear. Morris et al report a point prevalence of concurrency in the United States of between 5% and 13% for African American young men and 4% for African American young women [[10]Morris M. Kurth A.E. Hamilton D.T. et al.Concurrent partnerships and HIV prevalence disparities by race: Linking science and public health practice.Am J Public Health. 2009; 99: 1023-1031Crossref PubMed Scopus (236) Google Scholar]. As this estimate is a point prevalence, it likely underestimates concurrency over a longer period (i.e., in past 6 or 12 months). Doherty et al found among Latino youth in the United States that 27% of males and 14% of females reported having concurrent partners in the past 6 months [[16]Doherty I.A. Minnis A. Auerswald C.L. et al.Concurrent partnerships among adolescents in a Latino community: The mission district of San Francisco, CA.Sex Transm Dis. 2007; 34: 437-443PubMed Google Scholar]. Manhart et al in a random digit-dial survey of 18–39 years olds in Seattle found that between 21% and 35% of males and 12%–24% of females reported concurrent partners depending on the way concurrency was measured [[17]Manhart L.E. Aral S.O. Holmes K.K. Foxman B. Sex partner concurrency: measurement, prevalence, and correlates among urban 18–39-year-olds.Sex Transm Dis. 2002; 29: 133-143Crossref PubMed Scopus (113) Google Scholar]. Although multiple partners, concurrency, network characteristics, and the prevalence of infection within given networks are important to the spread of epidemics—we do not believe they are the sole driver of the epidemic observed in sub-Saharan Africa. With regard to race, we found race to be strongly associated with HIV in the data used in the SA-US comparison; in fact, young black South African women were almost eight times more likely to be infected compared with young women of other races [[18]Pettifor A.E. Rees H.V. Kleinschmidt I. et al.Young people's sexual health in South Africa: HIV prevalence and sexual behaviors from a nationally representative household survey.AIDS Lond Engl. 2005; 19: 1525-1534Crossref PubMed Scopus (450) Google Scholar]. However, as noted above, there are a host of biological, behavioral, and contextual/structural factors that likely explain this increased risk, not concurrency alone. We previously reported that young black South African women with one lifetime partner experience a remarkable risk of acquiring HIV, a phenomena not easily explained via sexual behavior alone [[19]Pettifor A.E. Hudgens M.G. Levandowski B.A. et al.Highly efficient HIV transmission to young women in South Africa.AIDS Lond Engl. 2007; 21: 861-865Crossref PubMed Scopus (40) Google Scholar]. Addressing sexual behavior is important to the control of the spread of HIV. However, the recognition that unique but poorly understood biological factors likely contribute to the spread of HIV in South Africa is also important for HIV prevention and to inspire greater compassion for the young people so greatly affected. Accordingly, we believe that addressing behavior alone will not be sufficient to eliminating the epidemic in sub-Saharan Africa. Combination HIV prevention, which addresses multiple risk factors at multiple levels at which risk occurs, seems like the most reasonable way forward [[20]Padian N.S. McCoy S.I. Karim S.S. et al.HIV prevention transformed: the new prevention research agenda.Lancet. 2011; 378: 269-278Abstract Full Text Full Text PDF PubMed Scopus (212) Google Scholar]. Sexual Behavior, HIV and South African YouthJournal of Adolescent HealthVol. 50Issue 2PreviewPettifor et al. recently compared sexual behavior self-reports and HIV prevalence in nationally representative samples of young people in South Africa (SA) and the United States [1]. They concluded that “young people in the US report riskier sexual behaviors than young people in SA, despite the much higher prevalence of HIV infection in SA. Factors above and beyond sexual behavior likely play a key role in ongoing transmission of HIV in South African youth, and thus should be urgently uncovered to develop maximally effective prevention strategies” (p. Full-Text PDF A Tale Of Two Epidemics Within TWO CountriesJournal of Adolescent HealthVol. 50Issue 2PreviewPettifor et al's recent study concludes that “the remarkable prevalence of HIV in young people in South Africa cannot be ascribed to exceptional risk taking behavior” [1]. This and the accompanying editorial [2] argue that behavioral change campaigns have “failed,” and that more emphasis needs to be placed on biological interventions. Full-Text PDF