The interconnectedness of HIV and other sexually transmitted diseases (STDs) grows more and more apparent as biomedical and behavioral scientists learn more about peopleís susceptibility and risks. CDC is applying new research to prevent all of the major STDs, including HIV infection, and to ensure that communities have the information they need to design, implement, and evaluate comprehensive approaches to HIV/STD prevention programming.
The Parallel Epidemics of HIV Infection and Other STDS
Globally, an estimated 333 million new cases of curable STDs1 occur each year among adults, according to 1995 estimates of the World Health Organization. STDs in the United States have reached epidemic proportions with an estimated 12 million new cases each year.2 Of these, 3 million occur among teenagers, 13 to 19 years old.
The spread of HIV in the U.S. through sexual transmission has paralleled that of other STDs. For example, the geographic distribution of the emerging problem of heterosexual HIV transmission in the South closely parallels that of syphilis. Most of the health districts with the highest syphilis and gonorrhea rates in the U.S. are concentrated in the southern part of the country, the same part of the Nation with the highest HIV prevalence among childbearing women. In addition, researchers have long recognized that the risk behaviors which place individuals at risk for other STDs also increase a personís risk of becoming infected with HIV. STD surveillance can provide important indications of where HIV infection may spread, and where efforts to promote safer sexual behaviors should be targeted.
Other STDs Facilitate HIV Transmission
There is now strong evidence that other STDs increase HIV transmission and, conversely, that STD treatment reduces HIV spread.
- Epidemiological studies: Prospective epidemiological studies have repeatedly demonstrated at least a twofold to fivefold increase in HIV transmission when other STDs are present.
- Biological studies: Biological studies suggest both increased susceptibility to HIV infection and increased likelihood of infecting other people when other STDs are present.
- a) Increased susceptibility -- Other STDs increase the number of HIV target cells (CD4 cells) in cervical secretions, thereby probably increasing HIV susceptibility in women.
- b) Increased infectiousness -- Studies have demonstrated that coninfection with HIV and other STDs results both in more shedding of HIV and in greater amounts of HIV being shed. For example, in African studies, coinfection with gonorrhea and HIV more than doubles the proportion of HIV-infected individuals with HIV RNA detectable in genital secretions. Furthermore, the median concentration of HIV RNA in semen is dramatically increased in coinfected men compared with men infected with HIV alone.
New Evidence for the Efficacy of STD Treatment in HIV Prevention
- Intervention studies: Exciting new evidence indicates that STD detection and treatment can substantially reduce HIV transmission. For example:
- a) STD treatment reduces the prevalence and magnitude of HIV shedding-- Treatment of gonorrhea in HIV-infected men reduces to baseline levels comparable to those in men who are not coinfected with HIV and other STDs both the proportion with and the concentration of HIV RNA detectable in semen.
- b) STD treatment reduces the spread of HIV infection in communities -- A community-level, randomized trial in a rural African community in Tanzania demonstrated a 42% decrease in new, heterosexually transmitted HIV infections in communities with improved STD treatment as compared to communities with minimal STD services. An ongoing randomized trial in Uganda is exploring alternative approaches, such as mass treatment, to look at the impact of STD control on HIV prevention. The results of these studies will be crucial to validating the findings of the Tanzanian trial and to providing a range of intervention models for reducing the spread of HIV infection in communities with high rates of other STDs both in the developing world and in industrialized countries like the United States.
Making the Numbers Count: Turning What We Have Learned into Prevention
CDC has a wide range of initiatives to reduce the spread of STDs and the attendant increased risk of the HIV transmission. Some of these include:
- New focus on syphilis in the south. "Innovations in Syphilis Prevention in the U.S.: Reconsidering the Epidemiology and Involving Communities" was initiated in October 1995 to develop innovative, practical, and community-involved STD prevention programs. This community-based approach to syphilis prevention is expected to contribute to HIV prevention in multiple ways that go beyond reducing the biological cofactor effect that syphilis represents for HIV transmission. It is expected to foster intramural and extramural collaboration on major CDC prevention research programs; implement research and development projects for syphilis elimination in the U.S.; and build collaborative intervention partnerships with communities that are affected by syphilis.
- Conducting and disseminating an inventory of innovative STD program activities that focus on STD prevention among adolescents. Special research and demonstration projects are underway to learn more about the behaviors, characteristics, and risk factors of youth at high risk, including those who are homeless, in detention, and in communities with high STD rates. Given the increasing levels of HIV infection among adolescents, these efforts are important strategies for changing this trend.
- Model STD intervention among Bolivian female sex workers that decreases HIV risk and transmission in a high risk community. A study in La Paz, Bolivia has demonstrated that intensive STD clinical and behavioral interventions among female sex workers in a resource-poor community both can reduce STD prevalence and maintain low HIV seroprevalence. This prevention model is now being replicated in other cities in Bolivia.
- Promoting skill development and enhancement for effective STD/HIV prevention efforts. CDC works to promote skill development for clinicians, educators, and trainers by providing training and networking opportunities that encourage professional growth and the refinement of prevention strategies among HIV/STD service providers.
- STD Accelerated Prevention Campaign offering opportunities for critical reevaluation and innovation in STD prevention programs. Twenty community-based STD innovative prevention projects have been funded, seven of which specifically target adolescents. This program enables health departments to implement and evaluate new, locally-relevant approaches to STD prevention that go beyond the traditional, clinic-based model. Populations benefiting from currently funded enhanced projects include women, adolescents, migrant farmworkers, and racial/ethnic minorities. Examples of innovative approaches that are being implemented and evaluated include: adolescent clinic services based in schools, detention centers, housing projects and other non-traditional sites; community-based outreach and peer education to such hard-to-reach populations as gang members; and STD prevention case management. Emphasis is placed on examining innovative, integrated models that incorporate HIV with STD prevention efforts.
- STD-Related Infertility Prevention Program. The STD-related Infertility Prevention Program is a cooperative effort between CDC and the Office of Population Affairs of the U.S. Public Health Service, and involves strong collaboration among family planning, STD, primary health care programs, and public health laboratories. The U.S. Congress allocated $8.3 million to initiate the program in 1993. The program seeks to establish high quality early detection and treatment services for women and their partners at risk for chlamydia infection and to provide screening and counseling, referral, follow-up, evaluation, and treatment for partners of women with chlamydia infection. In light of the increased risk of HIV transmission associated with chlamydial infection, these efforts will have an important complimentary effect on reducing HIV transmission.
In Vancouver, CDC will present updates on recent community-based efforts to prevent, diagnose, and treat STDs, as well as the latest research examining the relationship between HIV and other STDs -- both in terms of risk and prevention.
Declining Prevalence of Gonorrhea and Chlamydia in Female Sex Workers, Chiang Rai, Thailand, 1991-94, Peter H. Kilmarx.
Rapid Decline in Sexually Transmitted Disease Prevalence Among Brothel-based Sex Workers in La Paz, Bolivia: The Experience of Proyecto Contra Sida, 1992-1995, William C. Levine.
Heterogeneity of Heterosexual Transmission: The Role of Other STDs, Judith N. Wasserheit.
HIV/STD High Risk Behavior Surveys--Where are the Gaps and What Needs to be Done? Robert Brackbill.
Randomized Controlled Trial of Intensive Group Counseling to Reduce Risk Behaviors in High-Risk STD Clinic Patients, Bernard Branson.
HIV/STD Educator/Trainer Network, Dennis Jarvis.
Association of Penicillin Mass Treatment Program with Sexually Transmitted Diseases among Female Sex Workers in Indonesia, M. Ridaun Joesoef.
Additional Sources of Care for STD Clinic Patients: Implications for HIV/STD Prevention Efforts, Jean M. Lawrence.
Needs Assessment of the Technical Assistance (TA) and Training Needs of STD and HIV Prevention Programs in the United States, Kathleen A. Stark.
HIV Seroincidence Among Persons Attending Sexually Transmitted Disease Clinics in the United States, 1988-1995, Hillard Weinstock.