Studies may overestimate connection between PrEP, STIs
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An Australian study demonstrated that STI rates among men who have sex with men were high and increasing before they started taking PrEP and remained stable afterward.
Data from the study, which included more than 2,400 men who have sex with men (MSM) “suggest that studies that do not consider preexisting STI trends may overestimate the association of PrEP with STI incidence,” the researchers wrote in JAMA Network Open.
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“There have been concerns that use of PrEP may be followed by increased incidence of other STIs, such as chlamydia, gonorrhea and infectious syphilis, because of a reduction in condom use and/or increase in sexual partners,” Hamish McManus, PhD, an epidemiologist in the University of New South Wales’ surveillance evaluation and research program, and colleagues wrote. “In several high-income countries, PrEP rollout has been temporally associated with an increase in reporting of STI notifications among MSM.”
McManus and colleagues conducted a before-and-after analysis of a PrEP implementation cohort in New South Wales, Australia, and used STI testing data from 54 sexual health clinics and six primary care clinics in Australia. The study included a subcohort from a PrEP implementation study of HIV-negative MSM who received PrEP for the first time and who had two or more STI tests in the past year.
In all, 2,404 individuals were included in the before-and-after analysis. The STI positivity rate in the group was 52% (23.3% per quarter; 95% CI, 22.5%-24.2%) in the year following PrEP initiation with no significant trend (average rate ratio [RR] increase per quarter = 1.01; 95% CI, 0.99-1.02) compared with 50% positivity (20% per quarter; 95% CI, 19.04-20.95%) during the year before PrEP initiation.
The risk ratio for overall STI positivity was 1.17 (95% CI, 1.1-1.24; P = .001) and had an increase in quarterly STI positivity (RR = 1.08 per quarter; 95% CI, 1.05-1.11; P = .001 to 0.93 per quarter; 95% CI, 0.9-0.96; P < .001).
“Over longer periods of follow-up, in populations with low prior STI testing rates, STI incidence in men taking PrEP has been predicted to decline as increased PrEP-related testing substantially increases the detection and treatment of asymptomatic infection,” the researchers wrote. “Further modeling is needed using real-world PrEP and STI data to explore this question further because testing quarterly also has resource implications for health services and leads to increased antibiotic treatment, which is a concern as antimicrobial resistance is increasing.”
Perspective
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In the past several years, the United States has recorded an increasing number of STI cases. Many of these have affected the MSM population and some have speculated that this may be associated with the increasing use of PrEP, perhaps because of decreasing condom use or increasing sexual activity. Such claims have been refuted by others finding that PrEP use has not been accompanied by increasing unprotected sex. Probably one of the strongest studies on this question come from the accompanying paper from Australia. A subset of more than 2,400 MSM of the 9,700 in an ongoing cohort of PrEP users had data on STI incidence for at least 1 year before PrEP initiation and 2 years following beginning its use. Although STI rates were very high overall, about 50% annually, STI diagnoses did not increase after the start of PrEP. The authors speculate that in the cohort, condomless sex and multiple sexual partners were common both before and following PrEP initiation. The results underscore that although PrEP has clearly decreased HIV transmission, it does not decrease the risk of other STIs and that PrEP programs must continue to support regular STI screening and treatment.
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