Danish Study Finds Increased STI Diagnoses in PrEP Users, But Mainly Due to Increased Testing

In a recent study conducted in Denmark, scientists mapped the annual incidence of three bacterial sexually transmitted infections (STIs) - chlamydia, gonorrhea, and syphilis - in people attending sexual health clinics before and after initiating prophylactic anti-HIV medication (PrEP). The results of the study showed that infection rates in these populations were 1,151 TP3T higher than before PrEP was initiated; however, much of this increase was due to an increase in the number of tests performed.

Prior to initiation of PrEP, the average STI testing rate among respondents was approximately 50 tests per 100 persons per year (i.e., one test every two years), whereas after PrEP, the testing rate rose to three to four tests per year, with each test peaking within a few months of initiating PrEP. Taking this into account, the rate of diagnosis of any bacterial STI among PrEP users was only 351 TP3T higher than before PrEP, and the increase in syphilis did not reach statistical significance.

In addition, the researchers found that the number of tests began to increase from about 200 to 500 per 100 person-years about 10-20 weeks before people actually started using PrEP, even when the cost of PrEP was discounted at the time it was initiated.

Dr. Sebastian von Schreeb and his team at the University Hospital of Copenhagen say their study demonstrates evidence that PrEP directly leads to the theory of 'risk compensation'. Risk compensation is a theory put forward by some behavioral scientists that if people feel less anxious about taking a protective action, they tend to increase the associated risky behavior. In the early days of PrEP and U=U, some researchers feared that this would lead to a significant decline in condom use, which might eliminate some or all of the benefits of biomedical prevention.

However, the authors point out that their study suggests that this is not the case for PrEP and sexually transmitted infections. They state that if risk compensation were effective, it would be expected that the incidence of sexually transmitted infections would increase when people feel protected from HIV. However, since no such increase was seen, an alternative explanation was proposed, namely that changes in sexual risk-taking behavior caused people to engage in PrEP.

The data from this study are particularly reliable because of the thorough healthcare monitoring carried out in Denmark. Each citizen is given a unique civil registration number that links to a comprehensive database of microbiological test results. The Danish public health system began offering PrEP in 2018, and all those who started PrEP participated in a national prospective cohort study, DanPrEPD, and will continue as participants even if they stop PrEP.

One of the reasons PrEP users diagnose more STIs after starting PrEP is that prior to PrEP, people may have come in for testing only when they were symptomatic, the study showed. This study does not imply that PrEP leads to risk compensation; rather, it suggests that PrEP should be given when there is an increased risk of STIs, i.e., when it is most needed, which, the authors add, makes PrEP programs a key point of intervention, and it is therefore crucial to provide a safe and supportive environment, including comprehensive sexual health counseling.