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PrEP use consistent with CDC guidelines may reduce STIs among MSM

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May 23, 2017

The use of pre-exposure prophylaxis, or PrEP, for HIV prevention in addition to routine screening and treatment of sexually transmitted infections could reduce the incidence of these infections among men who have sex with men, even when condom use is reduced, according to the results of a modeling study recently published in Clinical Infectious Diseases.

Samuel Jenness, PhD, MPH, assistant professor of epidemiology at Emory’s Rollins School of Public Health, and colleagues reported that consistent PrEP use can reduce the risk for HIV by more than 95% among men who have sex with men (MSM); however, previous research has indicated that PrEP may be linked to a higher incidence of bacterial sexually transmitted infections (STIs). The researchers suggested that this may either be due to causal effects of PrEP or noncausal effects due to study biases. The primary causal hypothesis is that PrEP use increases behavioral risk compensation (RC), where MSM may reduce adherence to other disease prevention strategies.

“The potential for PrEP to increase STI incidence was a public health concern even before the completion of the clinical trials establishing its efficacy,” the researchers wrote. “The hypothesized cause for increased STI incidence would be different forms of RC, including an increase in the number of partners, greater clustering of higher risk men, or a reduction in condom use with existing partners. Few studies have found behavioral evidence for RC, but one that has suggested the predominant form of RC is reduced condom use.”

To address questions about potential causal effects of PrEP, Jenness and colleagues used a mathematical model to determine how many new asymptomatic and rectal cases of gonorrhea and chlamydia could be prevented if MSM initiated PrEP and received biannual bacterial STI testing and treatment, per the CDC’s clinical practice guidelines for PrEP.

The results, which were previously presented at CROI 2017, showed that if 40% of PrEP–eligible MSM initiated PrEP and underwent biannual screening, more than 40% of chlamydia infections and 42% of gonorrhea infections would be prevented over the next 10 years. This finding would occur even if a patient reduced condom use 40% while receiving PrEP. The researchers attributed the decline in STI incidence to an increase in the detection of asymptomatic (17%) and rectal cases (16%) that would subsequently be treated.

In additional analyses, Jenness and colleagues found that quarterly screening, rather than biannual screening, would result in a further 50% reduction in incidence of STIs.

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“Consistent with empirical data, we found that decreasing the STI screening interval from 6 to 3 months could identify even more incident infections that would otherwise go undiagnosed and untreated, suggesting more frequent PrEP–related screening may be needed,” they concluded. “These results underscore the critical role of clinicians in performing the STI screening and treatment recommendations among their current PrEP patients, as we predicted STI incidence could increase if the proportion of PrEP users treated for STIs fell below 50%.” – by Stephanie Viguers

Disclosure: The researchers report no relevant financial disclosures.

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