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The interconnectedness of HIV/AIDS, other sexually transmitted diseases (STDs), and tuberculosis (TB) grows increasingly apparent as biomedical and behavioral scientists learn more about people's susceptibility and risks. CDC is applying new research to the prevention of TB and all major STDs, including HIV infection, and is working to ensure communities have the information they need to design, implement, and evaluate comprehensive approaches to prevention of these diseases.

This page provides a basic overview of how HIV/AIDS, STDs, and TB are connected and how prevention strategies must recognize these connections.

There is now strong evidence that other STDs increase the risk of HIV transmission and, conversely, that STD treatment reduces the spread of HIV.

• Epidemiological studies: Studies have repeatedly demonstrated that people are 2-5 times more likely to become infected with HIV 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.
• Increased susceptibility: STDs that cause genital lesions can create a portal of entry for HIV. Even without lesions, STDs increase the number of HIV target cells (CD4 cells) in cervical secretions, thereby likely increasing HIV susceptibility in women.
• Increased infectiousness: Studies have demonstrated that co-infection with HIV and other STDs results both in more shedding of HIV and in greater concentrations of HIV being shed. For example, in African studies co-infection 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 co-infected men compared with men infected with HIV alone.

New Evidence of the Effectiveness of STD Treatment in HIV Prevention

New evidence indicates that STD detection and treatment can substantially reduce HIV transmission. For example:

• STD treatment reduces the prevalence and magnitude of HIV shedding. Treatment of gonorrhea in HIV-infected men resulted in a reduction in the number of men who shed HIV, as well as a lower concentration of HIV shed. With STD treatment, the level of shedding among co-infected men returns to the level seen in men who are not co-infected.
• 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. An ongoing study in Uganda is further exploring the impact of mass STD treatment in slowing the spread of HIV. These studies will be critical in more clearly defining the role STD treatment can play in HIV prevention efforts in the developing world and in industrialized nations.

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 HIV transmission. Some of these include:

• Guidelines development. During the summer of 1998, CDC's Advisory Committee for HIV and STD Prevention (ACHSP) will issue guidelines for local jurisdictions on the use of STD testing and treatment as an effective HIV prevention strategy in the United States.
• STD/HIV demonstration projects. CDC has awarded funds for demonstration projects in three areas of the country (North Carolina, Baltimore, and Louisiana) to provide on-site STD screening and treatment and related services in settings serving HIV-infected and at-risk individuals.
• Syphilis elimination. A national syphilis elimination effort will target the same areas of the country with increasing rates of heterosexually transmitted HIV infection. Because syphilis facilitates the transmission of HIV infection, syphilis elimination can have a significant effect on HIV transmission in many communities.
• STD-related Infertility Prevention Program. In 1998, the U.S. Congress allocated $17.5 million for infertility prevention. This program seeks to reduce infertility by improving the detection and treatment of chlamydia in women and their sexual partners. Chlamydia is a common STD that frequently goes undiagnosed in women, resulting in severe reproductive problems including infertility.
• Training programs. State training programs for STD and HIV staff are being targeted to areas with high rates of syphilis and gonorrhea. The training focuses on lessons learned from HIV community planning and the most effective use of STD screening and treatment.
• Comprehensive STD Prevention Systems (CSPS). Beginning in 1999, the CSPS Project Grants will expand requirements for comprehensive state and local STD programs. These state and local plans will concentrate on collaboration between public and private sectors; seek community involvement to accomplish STD prevention goals; focus on issues related to quality, access, and assurance; and harness recent advances in clinical, epidemiological, behavioral, and health services research. All programs are required to address the intersection of HIV with other STDs.

TB and HIV**

Tuberculosis is a disease that is spread from person to person through the air, and it is particularly dangerous for people infected with HIV. Worldwide, TB is the leading cause of death among people infected with HIV.

An estimated 10-15 million Americans are infected with TB bacteria, with the potential to develop active TB in the future. About 10 percent of these infected individuals will develop TB at some point in their lives. However, the risk of developing TB disease is much greater for those infected with HIV and living with AIDS. Because HIV infection so severely weakens the immune system, people dually infected with HIV and TB have a 100 times greater risk of developing active TB disease and becoming infectious compared to people not infected with HIV. CDC estimates that 10 to 15 percent of all TB cases and nearly 30 percent of cases among people ages 25 to 44 are occurring in HIV-infected individuals.

This high level of risk underscores the critical need for targeted TB screening and preventive treatment programs for HIV-infected people and those at greatest risk for HIV infection. All people infected with HIV should be tested for TB, and, if infected, seek preventive therapy as soon as possible to prevent TB.

Intersection of Two Global Epidemics

• Approximately 2 billion people (one-third of the world's population) are infected with Mycobacterium tuberculosis, the cause of TB.
• TB is the cause of death for one out of every three people with AIDS worldwide.
• The spread of the HIV epidemic has significantly impacted the TB epidemic. One-third of the increase in TB cases over the last five years can be attributed to the HIV epidemic (Source: UNAIDS).

Addressing the Dangers of the Interconnected STD/TB/HIV Epidemics Requires Expanded Efforts***

Control of these diseases is an exercise in vigilance. The goal of controlling and eventually eliminating TB requires a targeted and continuous effort to address the prevention and treatment needs for those most at risk, including HIV-infected individuals. Efforts to eliminate TB are therefore essential to reducing the global toll of HIV.

Testing and treatment of STDs can be an effective tool in preventing the spread of HIV. Consequently, HIV programs and STD testing and treatment programs should develop strong linkages. This is especially important for programs targeting sexually active young women, who represent one of the fastest growing populations with AIDS.

The NPIN Web site is a resource sponsored by the CDC National Center for HIV, STD and TB Prevention (NCHSTP) and is designed to facilitate the sharing of information and resources related to the prevention of HIV/AIDS, STDs, and TB.

Sources:

*CDC Update: Prevention and Treatment of STDs as an HIV Prevention Strategy
**CDC Update: The Deadly Intersection Between TB and HIV
***CDC Update: The Role of STD Detection and Treatment in HIV Prevention