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Testing and treatment of sexually transmitted
diseases (STDs) can be an effective tool in preventing
the spread of HIV, the virus that causes AIDS. An
understanding of the relationship between STDs and HIV
infection can help in the development of effective HIV
prevention programs for persons with high-risk sexual
behaviors .
What is the link between STDs and HIV infection?
Individuals who are infected with STDs are at least two
to five times more likely than uninfected individuals to
acquire HIV if they are exposed to the virus through
sexual contact. In addition, if an HIV-infected
individual is also infected with another STD, that
person is more likely to transmit HIV through sexual
contact than other HIV-infected persons (Wasserheit,
1992).
There is substantial biological evidence demonstrating
that the presence of other STDs increases the likelihood
of both transmitting and acquiring HIV (Fleming,
Wasserheit, 1999).
Increased susceptibility. STDs probably increase
susceptibility to HIV infection by two mechanisms.
Genital ulcers (e.g., syphilis, herpes, or chancroid)
result in breaks in the genital tract lining or skin.
These breaks create a portal of entry for HIV.
Non-ulcerative STDs (e.g., chlamydia, gonorrhea, and
trichomoniasis) increase the concentration of cells in
genital secretions that can serve as targets for HIV
(e.g., CD4+ cells).
Increased infectiousness. Studies have shown that when
HIV-infected individuals are also infected with other
STDs, they are more likely to have HIV in their genital
secretions. For example, men who are infected with both
gonorrhea and HIV are more than twice as likely to shed
HIV in their genital secretions than are those who are
infected only with HIV. Moreover, the median
concentration of HIV in semen is as much as 10 times
higher in men who are infected with both gonorrhea and
HIV than in men infected only with HIV.
How can STD treatment slow the spread of HIV
infection?
Evidence from intervention studies indicates that
detecting and treating STDs can substantially reduce HIV
transmission at the individual and community levels.
STD treatment reduces an individual's ability to
transmit HIV. Studies have shown that treating STDs in
HIV-infected individuals decreases both the amount of
HIV they shed and how often they shed the virus
(Fleming, Wasserheit, 1999).
STD treatment reduces the spread of HIV infection in
communities. Two community-level, randomized trials have
examined the role of STD treatment in HIV transmission.
Together, their results have begun to clarify conditions
under which STD treatment is likely to be most
successful in reducing HIV transmission. First,
continuous interventions to improve access to effective
STD treatment services is likely to be more effective in
reducing HIV transmission than intermittent
interventions through strategies such as periodic mass
treatment. Second, STD treatment is likely to be most
effective in reducing HIV transmission where STD rates
are high and the heterosexual HIV epidemic is young.
Third, treatment of symptomatic STDs may be particularly
important.
The first community trial, conducted in a rural area of
Tanzania, demonstrated a decrease of about 40% in new,
heterosexually transmitted HIV infections in communities
with continuous access to improved treatment of
symptomatic STDs, as compared to communities with
minimal STD services, where incidence remained about the
same (Grosskurth, Mosha, Todd, et al., 1995). However,
in the second trial conducted in Uganda, a reduction in
HIV transmission was not demonstrated when the STD
control approach was community-wide mass treatment
administered to everyone every 10 months in the absence
of regular access to improved STD services (Wawer, et
al., 1999).
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