Contribution of Viral and Bacterial STIs to HIV Acquisition

Observational studies along with longitudinal data have suggested that other sexually transmitted infections (STIs) increase the susceptibility to and infectiousness of HIV.1-4 Although many STIs appear to be associated with HIV, additional studies are essential to understand the relative importance of these STIs and whether STI exposures are present before the occurrence of HIV infection.5

To research this link between STIs and HIV, a nested case-control study examined the relative contribution of viral and bacterial STIs on HIV acquisition in women living in southern Africa.

Among the 33 million individuals infected with human immunodeficiency virus (HIV), more than two-thirds reside in sub-Saharan Africa.6-7 Young women aged 15-19 years are particularly vulnerable to HIV infection and are twice as likely to become infected as young men.8 At enrollment, women aged 18 to 49 years were tested for STIs such as chlamydia, gonorrhea, trichomoniasis, syphilis, HSV-2, HIV and pregnancy.9

Each participant received an HIV prevention package which included HIV risk reduction counseling and diagnosis and treatment of curable STIs. In addition, participants were asked to respond to questions on socio-demographic and behavioral factors. Through quarterly follow up during a 12-24 month period, participants received counseling and testing for HIV, gonorrhea, chlamydia, trichomoniasis, HSV-2 and HIV. Out of the 4948 women in the study, 309 incident HIV cases and 927 HIV-uninfected controls were analyzed.9
A number of risk factors were identified which increase the risk of HIV infection. Risky sexual behaviors such as multiple partners, use of alcohol and drugs before sex, and sex in exchange for food, drugs, money or shelter increased the risk of HIV infection. Furthermore, women whose partners engaged in high risk sexual behaviors were also at increased risk.

However, sociodemographic factors such as cohabitation with primary partners and giving birth to one or two children were associated with a lower risk of HIV infection.

Researchers found that women with certain STIs, specifically HSV-2 and gonorrhea, had a high risk of HIV infection.9 The adjusted population attributable fractions of HIV incidence were 29%, 4% and 2% for prevalent HSV-2, gonorrhea and incident HSV-2 infections respectively.9

These results indicate that the contribution of incident bacterial and viral STIs were significant risk factors for HIV acquisition. Therefore, avoidance of bacterial and viral STIs would result in a proportional reduction in HIV infection in the population.

This study is limited in some ways. Since STI and HIV acquisition is associated with similar risk factors, it is difficult to determine whether HIV infection was due to risk behaviors themselves or to the presence of STIs.
Regardless of these limitations, it is important to understand that both viral and bacterial STIs can contribute significantly to HIV risk.
Bacterial STIs such as gonorrhea may be easily curable, but may still increase risk of HIV infection. On the other hand, viral STIs such as HSV-2 may not be curable, and may accumulate risk in the population.

In order to control HIV infection, healthcare professionals need to understand and prevent viral and bacterial STIs. Creating more STI/HIV prevention interventions and early STI detection and treatment can reduce the risks of HIV acquisition.8 However, it is best to avoid the risk of STI and HIV infection by avoiding risk behaviors that contribute to these infections.
Abstinence from sexual activity until a person is in a lifelong relationship with an uninfected partner is the most effective approach to avoiding STIs and thus, HIV.


1 Røttingen J, Cameron DW, Garnett GP. A systematic review of the epidemiologic interactions between classic sexually transmitted diseases and HIV: how much really is known? Sex Transm Dis. 2001;28:579–597.

2 Fleming D, Wasserheit JN. From epidemiological synergy to public health policy and practice: the contribution of other sexually transmitted diseases to sexual transmission of HIV infection. Sex Transm Infect. 1999;75:3–17.

3 Grosskurth H, Gray R, Hayes R, Mabey D, Wawer M. Control of sexually transmitted diseases for HIV-1 prevention: understanding the implications of the Mwanza and Rakai trials. Lancet. 2000;355:1981–1987.

4 CDC. The Role of STD detection and Treatment in HIV prevention — CDC Fact Sheet. Available at: Accessed June 15, 2011.

5 Zetola N, Bernstein KT, Wong E, Louie B, Klausner JD. Exploring the relationship between sexually transmitted diseases and HIV acquisition by using different study designs. J Acquir Immun Defic Syndr. 2009;50:546–551.

6 WHO/UNAIDS 2010. Fast Facts on HIV. Available at: Accessed June 21, 2011.

7 UNAIDS. UNAIDS/WHO AIDS epidemic update. 2007. Available at: Accessed June 21, 2011.

8 Human Sciences Research Council. South African National HIV Prevalence, Incidence, Behavior, and Communication Survey, 2008: A Turning Tide Among Teenagers? Cape Town, South Africa: HSRC Press, 2008.

9 Venkatesh KK, Van der Straten A, Cheng H, et al. The relative contribution of viral and bacterial sexually transmitted infections on HIV acquisition in southern African women in the Methods for Improving Reproductive Health in Africa study. I J STD AIDS. 2011;22:218-224.

Reviewed: June 2011