The implications of expanding HIV pre-exposure prophylaxis (PrEP) coverage in men who have sex with men (MSM) on sexually transmitted infection (STI) epidemics vary depending on the benefit to the individual or the population, as well as the specific STI, according to a commentary published in Sexually Transmitted Diseases.1

There are roughly 3 ways that HIV PrEP may affect STI case detection. First, under the current HIV PrEP guidelines, MSM receiving HIV PrEP should be screened as frequently as 4 times a year. As a result, as HIV PrEP coverage expands, more STIs will be identified and treated independently of changes in incidence. Second, HIV PrEP may change sexual behavior in a way that facilitates STI transmission (such as reduced condom use or an increase in the number of partners). Third, MSM receiving HIV PrEP may have higher rates of reinfection since they will be screened more frequently than individuals not receiving PrEP. 

Regardless of the mechanism by which HIV PrEP may lead to an increase in reported STI case rates at the individual level, increased routine screening for syphilis and gonorrhea in MSM on HIV PrEP will be beneficial “through prompt treatment of those infected, eliminating acute symptoms and possibly reducing sequelae and onward transmission to sex partners,” noted the study authors.

However, the population-level benefit may be limited with new infections effecting a change in sexual behavior and frequent reinfections with associated increases in highly infectious periods for syphilis, which may lead to an increase in STIs in sexual networks. When considering gonococcal infections, a network-based mathematical model found that HIV PrEP implementation could avert 42% of infections if 40% of MSM eligible for HIV PrEP received it; the same model also found that with substantial change in sexual behavior, such as a significant reduction in condom use and low HIV PrEP coverage, gonorrhea incidence could exceed reported rates prior to HIV PrEP implementation.2

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Further, the population-level benefit of HIV PrEP on STI epidemics in MSM may be diminished if it coincides with the development of antimicrobial-resistant gonorrhea or increased spread of STIs to heterosexual networks.

Along with considering the health benefits for individuals, public health programs should focus on health benefits for the population. “Further research is needed to determine the optimal STI screening frequency for MSM, regardless of HIV PrEP use, as a means to prevent and control STIs, as well as the potential benefit of STI PrEP (eg, prophylactic doxycycline to prevent bacterial STIs) to reduce STIs among MSM,” concluded the researchers.

References

1. Grey JA, Torrone EA, Sullivan PS, Weiss KM, Aral SO. Population and individual-level effects of human immunodeficiency virus preexposure prophylaxis on sexually transmitted infection epidemics among men who have sex with men. Sex Transm Dis. 46(12):759-761.

2. Jenness SM, Weiss KM, Goodreau SM, et al. Incidence of gonorrhea and chlamydia following human immunodeficiency virus preexposure prophylaxis among men who have sex with men: a modeling study. Clin Infect Dis. 2017;65(5):712-718.