Infectious Disease

Research can overestimate the connection between PrEP and STIs

January 07, 2021

2 min read

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McManus does not report any relevant financial information. In the study you will find all relevant financial information from all other authors.

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An Australian study showed that STI rates in men who have sex with men were high and rising before they started taking PrEP and remained stable afterwards.

Data from the study, which included more than 2,400 men who have sex with men (MSM), “suggests that studies that ignore pre-existing STI trends may overestimate the association of PrEP with STI incidence” wrote the researchers in JAMA Network Open.

PrEP pill

Many studies may consider non-existent STI trends and overestimate the association between PrEP use and STI incidence.
Photo credit: Adobe Stock

“There were concerns that PrEP use could be followed by an increased incidence of other sexually transmitted diseases such as chlamydia, gonorrhea and infectious syphilis due to a decrease in condom use and / or an increase in sexual partners.” Hamish McManus, PhD, An epidemiologist in the University of New South Wales Evaluation and Research Program for Surveillance and colleagues wrote. “In several high-income countries, the introduction of PrEP was temporally associated with an increase in the reporting of STI notifications to MSM.”

McManus and colleagues performed a before and after analysis of a PrEP implementation cohort in New South Wales, Australia, using STI test data from 54 sexual health clinics and six primary care clinics in Australia. The study included a sub-cohort from a PrEP implementation study in HIV-negative MSM who was receiving PrEP for the first time and who had two or more STI tests in the past year.

A total of 2,404 people 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 after the start of PrEP with no significant trend (average rate ratio) [RR] Increase per quarter = 1.01; 95% CI, 0.99-1.02) compared to 50% positivity (20% per quarter; 95% CI, 19.04-20.95%) in the year before the start of PrEP.

The risk ratio for overall STI positivity was 1.17 (95% CI, 1.1-1.24; P = 0.001) and increased quarterly STI positivity (RR = 1.08 per quarter; 95% CI, 1, 05-1.11; P = 0.001) to 0.93 per quarter; 95% CI, 0.9-0.96; P <0.001).

“Over extended periods of follow-up in populations with low STI test rates, the incidence of STI has been predicted to decrease in men taking PrEP as increased PrEP-related tests significantly improve the detection and treatment of asymptomatic infections,” the researchers wrote . “More modeling using real-world PrEP and STI data is needed to further investigate this question, as quarterly testing also impacts health care resources and leads to increased antibiotic treatment, which is a problem with increasing antibiotic resistance.”

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Paul A. Volberding, MD)

Paul A. Volberding, MD

In recent 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 could be linked to the increased use of PrEP, possibly due to decreased condom use or increased sexual activity. Such claims have been refuted by others who found that the use of PrEP was not associated with an increase in unprotected sex. Probably one of the strongest studies on this question comes from the accompanying paper from Australia. A subgroup 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 starting PrEP and 2 years after starting their use. Although the overall STI rates were very high, around 50% per year, the STI diagnoses did not increase after the start of PrEP. The authors speculate that condomless sex and multiple sexual partners were common in the cohort both before and after PrEP initiation. The results underscore that while PrEP has significantly reduced HIV transmission, it does not reduce the risk of other sexually transmitted diseases and that PrEP programs must continue to support the regular screening and treatment of sexually transmitted diseases.

Paul A. Volberding, MD

Editor-in-Chief, Infectious Disease News

Professor of Medicine

Director of the AIDS Research Institute

University of California, San Francisco

Disclosure: Volberding reports that he chairs a data security supervisory board at Merck and advises Gilead Sciences.

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