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STIs: What Role Do They Play in HIV Transmission?

Summer 2012

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Public Health Strategies Used to Prevent HIV

STIs may also decrease the effectiveness of public health strategies being rolled out to reduce new HIV infections in Canada. One example is the use of antiretroviral treatment as an HIV prevention strategy. (This strategy is also referred to as a "test and treat," "treatment as prevention," "seek and treat" or "testing and linkage to care (TLC)" strategy.) The goal of this strategy is to increase the number of people living with HIV who are on treatment and have an undetectable blood viral load, in order to decrease the overall viral load in a population (also known as the "community viral load"). Research suggests that a lower "community viral load" is associated with reductions in HIV transmissions in a population.8

Alarmingly, a high prevalence of STIs among people living with HIV may undermine the effectiveness of this strategy.5,9 This is because having an STI can lead to a person having a high level of HIV in their genital or rectal fluids, even if the virus level is low or undetectable in their blood. This makes it more difficult for the "test and treat" strategy to prevent HIV transmissions.

STI Prevention Is an Important Component of HIV Prevention -- or Is It?

It is generally believed that the management of STIs should be an essential component of a comprehensive approach to HIV prevention. Reducing the infection rates and prevalence of STIs -- through improved STI prevention, diagnosis and treatment -- may help reduce the number of new HIV infections that occur in Canada each year.

However, research studies investigating whether improved management of STIs can reduce new HIV infections have produced mixed results.10 All of these studies were carried out in heterosexual communities in Africa, and most showed that STI prevention and treatment is not a successful HIV prevention strategy. It is not completely clear why, but some researchers believe this may be the result of poor study design or other factors, such as:

  • the stage of the epidemic in the population being studied (STI management may be more effective in curtailing an emerging epidemic compared to one that is more generalized throughout the population)11
  • poor adherence to STI treatments among the study participants12
  • ongoing residual inflammation that remains during/after STI treatment13

Because evidence suggests that STIs increase the risk of HIV transmission, we expect that improving the management of STIs in a population would reduce HIV transmission. But only one out of seven randomized controlled trials exploring STI prevention and treatment as a potential HIV prevention strategy found that this was the case.

The successful study was conducted in a region of Tanzania in East Africa.14 In this study, STI management was improved in six "intervention" communities through the establishment of an STI reference clinic, staff training, drugs to treat STIs, regular supervisory visits to health facilities, and health education about STIs. After two years, the number of new HIV infections in the six "intervention" communities was 42% lower than the six similar "control" communities, where STI management was not improved.

Surprisingly, six other studies seem to suggest that the prevention and/or treatment of STIs is not an effective strategy to reduce HIV transmissions.15-20 The study design of three of these was similar to the design of the Tanzanian study but these studies took place in Zimbabwe16 and Uganda.15,18 These studies found that the number of new HIV infections was not lower in "intervention" communities than in "control" communities. Another study found that sex workers in Kenya who took regular antibiotic pills to prevent bacterial STIs were no less likely to become infected with HIV than sex workers who took a placebo pill.17

The remaining two studies looked at whether the treatment of herpes is an effective HIV prevention strategy.19,20 These studies enrolled both HIV-negative and HIV-positive individuals infected with herpes. Compared to individuals taking a placebo pill, the use of daily acyclovir (the drug used to treat herpes) did not protect HIV-negative individuals infected with herpes from becoming infected with HIV or prevent HIV-positive individuals co-infected with herpes from transmitting HIV to someone else.

Improving the Control of STIs -- What Can We Do?

Regardless of the role STIs play in HIV transmission, the management of STIs is critical. STIs can be painful, unpleasant and, in some cases, cause serious complications, such as anal and cervical cancer and infertility. Some STIs can also cause problems during pregnancy and be transmitted from a pregnant woman to her baby during birth.

Community-based organizations have a key role to play in preventing the spread of STIs and encouraging people to get tested and treated. Community-based organizations can contribute to the control of STIs in various ways:

  1. Awareness campaigns
    Campaigns that increase people's awareness of the risks, symptoms and spread of STIs, and of the importance of STI treatment, may help reduce the behaviours that put people at risk and encourage regular STI testing.

    Several awareness campaigns have been developed across Canada. One example is the recent "Attack of the cursed syphilis" campaign, originally developed by the AIDS Committee of Toronto (ACT) and further redeveloped by ACT and The Gay Men's Sexual Health Alliance, and later disseminated nationally by CATIE through funding from the Public Health Agency of Canada.
  2. Counselling and educational workshops
    During counselling and group workshops, community-based organizations can communicate key messages about the prevention and management of STIs, for example:
    • Condoms (female and male condoms), when used correctly, are the most effective method of preventing the transmission of STIs and HIV.
    • If a person is engaging in any type of sexual activity, it's important to get tested regularly for HIV and STIs.
    • If a person tests positive for HIV they should be tested for STIs, and vice versa
    • If a person suspects they are infected with an STI, they should get tested and, if they test positive, seek treatment as soon as possible. Leaving an STI untreated may not only increase their risk of HIV and STI transmission, but also make the STI more difficult to treat and could lead to other complications.
    • Although only some STIs are curable, they are all treatable. Management of incurable STIs -- such as herpes and genital warts -- through treatment may help reduce inflammation and other symptoms, as well as the risk of HIV and STI transmission.
    • For people living with HIV, STIs may take longer to treat and also speed up the rate at which HIV weakens the immune system.
  3. Advocacy
    Advocacy may be needed to improve access to appropriate and non-judgmental sexual health services, particularly for marginalized populations and people who live in rural areas.


STIs are on the rise in Canada, and remain an important public health concern. There is plenty of evidence to suggest that they can contribute to an overall increase in HIV transmission. Although there is mixed evidence on whether the management of STIs is an effective HIV prevention strategy, there are several ways in which community-based organizations can help stem the continuing rise of STIs in this country.


High Prevalence of Sexually Transmitted Infections Among People Living With HIV -- Implications for HIV Prevention -- CATIE News

Sexually Transmitted Infections and HIV Transmission -- CATIE fact sheet

About HIV and STIs -- Health Initiative for Men (HIM)

James Wilton is the Project Coordinator of the Biomedical Science of HIV Prevention Project at CATIE. James has an undergraduate degree in Microbiology and Immunology from the University of British Columbia.

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This article was provided by Canadian AIDS Treatment Information Exchange. It is a part of the publication Prevention in Focus: Spotlight on Programming and Research. Visit CATIE's Web site to find out more about their activities, publications and services.
See Also
Quiz: Are You at Risk for HIV?
Ten Common Fears About HIV Transmission
Is HIV the Only Incurable Sexually Transmitted Disease?
The HIV-STD Connection
More on Sexually Transmitted Diseases

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