Definition of the Prevention Area
Sexually transmitted infections (STIs) likely facilitate HIV transmission and acquisition. STI treatment activities have been used as an HIV prevention approach, but have achieved mixed outcomes. This prevention strategy may be most effective in settings with a high burden of STIs, and when targeted to members of key populations and their sexual partners. However, randomized trials have found STI treatment to have little to no effect on HIV incidence.
Epidemiological Justification for the Prevention Area
The role of STIs in the transmission dynamics of HIV epidemics is paradoxical and complex. Population-based studies have found that both the prevalence and incidence of HIV were substantially higher among people with STIs. Both curable STIs and chronic infections, such as herpes simplex virus type-2 (genital herpes), can increase vulnerability to HIV infection by disrupting skin and mucosal barriers and/or by causing inflammation, which brings HIV-susceptible immune cells to the genital tract. STIs are biological markers for risky sexual behaviors, which are also risk factors for HIV acquisition.
Also, a number of studies in HIV-serodiscordant couples report that HIV-positive individuals with herpes or genital ulcer disease are significantly more likely to transmit HIV to their partners. Some STIs appear to increase the risk of HIV transmission by boosting viral shedding in the genital secretions of both men and women who are HIV-positive. Other studies of HIV-positive individuals on antiretroviral therapy suggest that STIs may increase the infectiousness of HIV, even when an individual has an undetectable viral load.
Despite these data, numerous clinical trials have been unable to demonstrate a decline in HIV incidence as a result of STI treatment. Some hypothesize that treated STIs may still cause inflammation and other changes in the genital mucosa, even after the initial symptoms have disappeared. Ongoing inflammation and changes in the genital mucosa following treatment may explain why STI treatment has no effect on HIV incidence; other possible factors include epidemic stage, prevalence of viral versus bacterial STIs, and type of treatment.
Core Programmatic Components
Even though STI treatment does not seem to have a significant impact on HIV incidence, effective management of STIs is an essential public health activity, especially for improved maternal and child health outcomes. Data linking the prevalence of STIs with increased risk of HIV transmission and acquisition underscore the importance of STI prevention, which can best be achieved through a comprehensive STI control program.
A 2009 review of STI control and HIV prevention in the Bulletin of the World Health Organization concluded that the core elements of a comprehensive STI control program should include:
- Reaching out to populations at greatest risk, particularly those who change partners frequently and thus may propel transmission within the population
- Promoting safer sex by providing condoms and conducting other prevention activities
- Offering effective clinical interventions (including STI screening, treatment, and case management)
- Initiating structural interventions to ensure an environment that supports safer sexual behavior and care- and treatment-seeking behaviors
- Collecting reliable data to monitor disease trends and the effectiveness of interventions.
Current Status of Implementation Experience
Research on how STIs modify HIV transmission is ongoing. Development of improved screening strategies to detect some asymptomatic STIs in resource-limited settings remains a research priority. Currently, STI treatment as a stand-alone HIV prevention intervention in generalized epidemics is not supported by scientific data.
The approach for STI control for HIV prevention depends on the type of HIV epidemic and the populations at highest risk. A number of resource-limited countries, including Cambodia, Kenya, Senegal, Sri Lanka, and Thailand, have demonstrated that it is feasible for programs to expand STI control services. Several countries that have successfully controlled STIs have also reported stabilization or reversal of their HIV epidemics. For instance, in India, the Avahan Initiative reported a reduction in STI and HIV incidence after it included improved delivery of STI management to key groups as part of its comprehensive prevention interventions. Thailand’s 100% Condom Programme appears to have contributed to both STI reduction and HIV prevention by requiring condom use in brothels.
The U.S. President’s Emergency Plan for AIDS Relief (PEPFAR) supports several approaches for STI control for HIV prevention, depending on epidemic type and population. In concentrated epidemics, the population focus should be on key populations, individuals with symptomatic STIs, HIV-positive persons with high-risk behaviors, and other groups that may be at high risk for STI acquisition. In generalized epidemics, PEPFAR supports STI control programs for high-risk subpopulations, including key populations, individuals with symptomatic STIs, HIV-positive persons, and sexually active adolescents. STI screening, management, and treatment are key components of the PEPFAR comprehensive package of services for key populations. PEPFAR also supports HIV testing services for STI patients.