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HIV Prevention Knowledge Base

A Collection of Research and Tools to Help You Find What Works in Prevention

Biomedical Interventions: Diagnosis and Treatment of Sexually Transmitted Infections

I. Definition of the Prevention Area

Sexually transmitted infections (STIs) likely facilitate HIV transmission and acquisition. STI treatment efforts have been used as an HIV prevention approach with mixed outcomes. This prevention strategy may be most effective in settings with a high burden of STIs and when targeted to most-at-risk populations and their sexual partners. However, randomized trials have found STI treatment to have little to no effect on HIV incidence.

II. 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 in 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 that 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.

In addition, 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 not been able 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. The ongoing inflammation and changes in the genital mucosa may be why STI treatment does not have an effect on HIV incidence. Epidemic stage, prevalence of viral versus bacterial STIs, and type of treatment may also be reasons that STI treatment does not lower HIV incidence.

III. Core Programmatic Components

While STI treatment does not seem to have a significant impact on HIV incidence, effective management of STIs is an essential public health activity and is particularly important 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.

The U.S. President’s Emergency Plan for AIDS Relief (PEPFAR) supports STI control for HIV prevention depending on epidemic type and population. In concentrated epidemics, the population focus should be on most-at-risk 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 most-at-risk populations, individuals with symptomatic STIs, HIV-positive persons, and sexually active adolescents. PEPFAR also supports HIV testing and counseling services for STI patients.

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, potentially propelling transmission within the population
  • Promoting safer sex through the provision of condoms and other prevention activities
  • Offering effective clinical interventions (including STI screening, treatment, and case management)
  • Initiating structural interventions to ensure an environment that supports safer sex behavior and care- and treatment-seeking behaviors
  • Collecting reliable data to monitor disease trends and the effectiveness of interventions.

IV. Current Status of Implementation Experience

Research is ongoing to better understand how STIs modify HIV transmission. The 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.

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 the improved delivery of STI management to most-at-risk groups as part of its comprehensive prevention interventions. Thailand’s 100% Condom Program appears to have contributed to both STI reduction and HIV prevention by requiring condom use in brothels. STI screening, management, and treatment are key components of the PEPFAR comprehensive package of services for most-at-risk populations.