Chlamydia and Gonorrhea Responsible for 10% of New HIV Infections Among MSM, According to New Study

Neisseria gonorrhoeae bacterium, which causes gonorrhea.
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A new study published January 19 in the journal Sexually Transmitted Diseases estimates that 10% of new HIV cases among men who have sex with men (MSM) are caused by existing gonorrhea or chlamydia infections. While the number of new HIV cases among MSM has remained fairly stable, sexually transmitted infections (STIs) are at an all-time high and threaten to make HIV prevention harder.

Chlamydia and gonorrhea are the two most common reportable STIs in the United States, and the rates are rising among men. In 2017, there were 363.1 cases of chlamydia per 100,000 men. This represents a 39% increase from just four years earlier in 2013. The gonorrhea rate among men rose even more (83%) during that same time period, from 108.7 to 202.5 cases per 100,000 men. Data suggest that the incidence of these and other STIs is higher in MSM than in men who have sex only with women.

HIV diagnoses have fallen among injection drug users and heterosexuals since 2012. They have also fallen among white gay and bisexual men but have remained stable among African-American gay and bisexual men, while increasing among Latino gay and bisexual men. Overall, the HIV rates remain unchanged among MSM.

People who have other STIs are known to be at greater risk of HIV. First and foremost, the same behaviors -- such as sex without a condom or multiple partners -- put individuals at risk for both. In addition, among MSM, transmission often occurs across the same network of sexual partners. There are biological factors as well; sores or inflammation caused by STIs like chlamydia and gonorrhea may allow HIV acquisition that would have been stopped by intact skin, and infections can bring more HIV target cells to the area. In addition, the presence of another STI in an HIV-positive person can increase viral shedding, making them more likely to transmit the virus.

It has been hard for researchers, however, to untangle these behavioral and biological components to determine the direct causal effect that STIs have on HIV risk. Chlamydia and gonorrhea are site-specific and can infect the throat, genitals, or anus. To truly determine the impact of these STIs on HIV transmission in MSM, therefore, researchers have to take into account which partner has an STI and where in the body this infection is present, as well as which partner is HIV-positive and the specific behaviors the couple engages in, including whether each is the insertive and/or receptive partner.

For this study, researchers used agent-based modeling that took all of these factors into account. The behavioral variables in the model, such as specific sexual behaviors and frequency of condom use, were based on data collected for a study of sexual networks in Atlanta, Georgia.

The researchers conducted separate analyses to isolate the effects of STIs on HIV transmission (scenarios in which the HIV-positive partner also had chlamydia or gonorrhea) and on HIV acquisition (scenarios in which the HIV-negative partner has one of these STIs). These analyses are particularly important, because they can help public health experts better tailor prevention efforts. If, for example, STIs prove to have a stronger impact on acquisition, creating interventions to reach HIV-negative men would be more effective, and vice versa.

Based on these calculations, researchers estimate that among MSM, between 3% and 20% of HIV transmission and between 2% and 15% of HIV acquisition is attributable to gonorrhea and chlamydia infection. This means that 10% of new HIV infections among MSM are due to these bacterial STIs, which translates to 2,600 HIV infections each year that could be averted if we were better able to screen for, treat, and ultimately prevent the spread of gonorrhea and chlamydia.

This study underscores the need for STI screening and prevention programs as part of the overall HIV-prevention strategy. Unfortunately, for more than a decade, funding for STI prevention has been cut on both state and federal levels. The National Coalition of STD Directors notes that the Centers for Disease Control and Prevention (CDC) STI program has suffered multiple budget cuts, which have resulted in a 40% reduction in buying power since 2003. And the CDC notes that in 2012, 52% of state and local STI programs experienced budget cuts that resulted in cuts to clinic hours, partner tracing, and STI screenings -- and at least 21 local health department STI clinics closed that year.

David C. Harvey, executive director of the National Coalition of STD Directors, has described this country's STI prevention infrastructure as "running on fumes." Health departments are being asked to do more with fewer resources than they had 15 years ago. In a statement, Harvey said, "This study highlights a clear need for a federal investment in the STD field and serves as a stark reminder that HIV and STD prevention must go hand-in-hand." He added, "The historic levels of STDs imperil our progress towards ending HIV. We can't hope to end HIV without also addressing STDs."