PrEP and STDs, Hidden and Obvious

The Conference on Retroviruses and Opportunistic Infections (CROI) occurred in Seattle from Feb. 13 through Feb. 16. Several sessions focused on the relationship of Pre-Exposure Prophylaxis (PrEP) to sexually transmitted diseases (STDs).

Opponents of PrEP have argued that PrEP would drive down condom use, increasing the risk for other STDs. Researchers at CROI reported that they failed to find evidence linking PrEP to increases in STDs. Researchers found some evidence that the structured care of PrEP could detect STDS with non-obvious symptoms. This increased detection and treatment of these hidden STDs could break the STD transmission cycle.  

STDs can be viral, bacterial, or parasitic. Researchers focused on the bacterial STDs: chlamydia, gonorrhea, and syphilis. Bacterial STDs vary in the obviousness of their symptom. Penile gonorrhea usually has obvious symptoms, but rectal chlamydia and rectal gonorrhea usually do not. Syphilis produces sores at the point of infection, but a rectal syphilitic sore may be invisible. As the symptoms of an STD drive people to be tested, hidden STDs frequently remain untreated. These untreated hidden STDs can still infect sexual partners. As anal infections with bacterial STDs tend to be hidden, these STDs pose a health risk to gay and bi men.

Dr. Matthew Golden reported on syphilis. From 1996 to 2015, 74 percent of all syphilis cases in the U.S. occurred among gay and bi men. Syphilis has occurred largely among gay and bi men with HIV. From 2011 to 2016, however, four cities reported a decline in the proportion of syphilis cases among gay and bi men with HIV. Seattle, San Francisco, New York, and Los Angeles, all experienced this decline. Seattle experienced an increase in the proportion of syphilis cases among gay and bi men without HIV. Golden recommended opt-out syphilis testing in HIV clinics, as a control measure.  

While gay and bi men have driven the syphilis epidemic, it may change. Gay and bi men from Florida, North Carolina, and Texas reported about 2 to 3 times more sex with women, than did gay and bi men from New York and Washington. This could lead to increased regional and racial health disparities. More research is needed on possible regional variations in bisexual behavior.  

Golden reported that the impact of PrEP on STDs was mixed and inconclusive. Golden concluded that PrEP would likely increase STD risk at the population level, but the “magnitude of that change is uncertain.” 

Dr. Michalina Montaño reported that diagnoses of STDs increased after people started PrEP. Montaño also found decreased condom use and increased diagnoses of chlamydia and gonorrhea. 

Montaño contrasted diagnoses between the obvious STDs and the hidden STDs. People with a hidden STD are less likely to seek testing and treatment. The structured medical care of PrEP, however, would diagnose and treat these STDs. This contrast could tease apart the effects of reduced condom use from those of increased diagnoses and treatment of hidden STDs.  

Montaño found major differences between these two groups. While diagnoses of the obvious STDs decreased by 17 percent, diagnoses of the hidden STDs increased by 140 percent. Increased diagnoses of rectal chlamydia largely drove the increase among the hidden STDs. Fewer diagnoses of syphilis largely drove the decrease among obvious STDs.

Single studies cannot provide definitive conclusions. In addition, African-Americans made up only 7.8 percent of this study. It will take more research to understand the relationship between PrEP and increased STD rates. These reports show that this relationship is not simple.

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