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CATIE News - High prevalence of sexually transmitted infections among people living with HIV - implications for HIV prevention

2011 Aug 22 - The sexual transmission of HIV occurs after an exposure to fluids that contain HIV, such as semen, vaginal fluid or rectal fluid. Research shows a higher amount of HIV (viral load) in these fluids increases the risk of HIV transmission, while a lower amount of HIV decreases the risk of HIV transmission.

Impact of STI co-infection on HIV transmission

Sexually transmitted infections (STIs)-such as gonorrhea, chlamydia, herpes and syphilis-can increase the HIV viral load of a person who is co-infected with HIV and an STI. Research shows that the location of the STI determines which bodily fluid is affected. For example, a rectal STI can increase the amount of HIV in the rectal fluid. Therefore, STI co-infection may increase the risk of a person passing HIV to others through unprotected sex.

It is also well documented that HIV-negative individuals who have an STI are at increased risk of becoming infected with HIV.

A recent systematic review explored the prevalence of STIs among people living with HIV. The high prevalence of STI/HIV co-infection found in this review has important implications for the transmission and prevention of HIV.

Study details

The authors of the review searched for studies that reported the prevalence of STIs among people living with HIV. The authors only included studies reporting the prevalence of STIs that are known to increase HIV transmission, including syphilis, chancroid, gonorrhea, chlamydia, herpes (HSV-2), trichomoniasis, bacterial vaginosis, urethritis and cervicitis.

The search identified 37 studies, which were included in the review. Most of the studies were from the United States and Europe. Nineteen of the 37 studies enrolled people living with HIV from North America. The studies included a total of 708,296 people living with HIV. One study from New York City accounted for approximately 90% of these individuals.


Overall, an average of 16.3% of the people living with HIV were co-infected with an STI. The average prevalence by type of STI was as follows:

  • Syphilis - 9.5%
  • Gonorrhea - 9.5%
  • Chlamydia - 5%
  • Trichomoniasis - 18.8%

STI rates were similar among men and women living with HIV.

STIs were more prevalent among individuals who were newly diagnosed with HIV. The average prevalence of STI infection among those individuals who learned of their positive HIV status when they were getting tested for STIs was 19.6%.

There was no difference in the prevalence of STIs among individuals receiving HIV treatment compared to those who were not on HIV treatment.

Only one Canadian study, published in 2009, was included in the review. This study enrolled 455 men and 174 women from infectious disease clinics in Edmonton, Quebec and Toronto. The prevalence of HIV/herpes co-infection among participants was 54%. Of the people infected with herpes, 58% did not have symptoms associated with herpes.

Implications for HIV prevention

The high prevalence of STIs among people living with HIV is concerning because it may be facilitating the transmission of HIV. This systematic review is a reminder that regular STI prevention counselling, testing (even in the absence of symptoms) and treatment are important components of HIV prevention.

The high prevalence of HIV/STI co-infection also has implications for counselling people about the risk of HIV transmission. The risk factors for the transmission of many STIs are not the same as those for HIV. Strategies that some people may use to reduce their risk of HIV transmission, such as serosorting, PrEP or treatment as prevention, may not reduce their risk of STI transmission. If the use of these strategies leads to the transmission of STIs, people may be inadvertently increasing the overall risk of HIV transmission.

Implications for "treatment as prevention"

The authors of the review were particularly concerned about whether or not the high prevalence of HIV/STI co-infection could undermine the effectiveness of using "treatment as prevention" because of an increased risk of HIV transmission in the presence of another STI.

People using HIV "treatment as prevention" may feel a false sense of security and engage in more risky behaviours-such as using fewer condoms or increasing their number of partners. This is also known as risk compensation. Risk compensation is a concern because HIV treatment does not completely eliminate the risk of transmitting HIV or reduce the risk of becoming infected with an STI. Therefore, risk compensation may further increase the prevalence of HIV/STI co-infection and reduce the effectiveness of "treatment as prevention."

The authors suggest that all individuals who are using HIV treatment to reduce their risk of transmitting HIV should "receive routine STI screening every three to four months" and "repeated counselling to address erroneous beliefs regarding infectiousness." Counselling should include discussing the importance of condom use in reducing both HIV and STI transmission.

-James Wilton


  1. Johnson LF, Lewis DA. The effect of genital tract infections on HIV-1 shedding in the genital tract: a systematic review and meta-analysis. Sexually Transmitted Diseases . 2008 Nov;35(11):946-59.
  2. Kalichman S, Pellowski J, Turner C. Prevalence of sexually transmitted co-infections in people living with HIV/AIDS: systematic review with implications for using HIV treatments for prevention. Sexually Transmitted Infections. 2011 Apr;87(3):183-90.



CATIE-News is written by Sean Hosein, with the collaboration of other members of the Canadian AIDS Treatment Information Exchange, in Toronto.

From Canadian AIDS Treatment Information Exchange (CATIE). For more information visit CATIE's Information Network at


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