Among men who have sex with men using event-driven PrEP or no PrEP, “PrEP surfing” was reported at one-quarter of study visits, according to a study published in AIDS.
The prospective study examined PrEP surfing among men without HIV who have sex with men participating in the Amsterdam Cohort Studies between October 2021 and December 2023. PrEP surfing was defined as using a partner’s PrEP use as a perceived HIV prevention strategy when engaging in condomless anal sex with that partner. Investigators assessed both recent PrEP surfing with casual partners and participants’ intention to practice it in the following 6 months.
Study design and participants
The analysis of intention included 2,187 visits from 636 participants. For the analysis of recent PrEP surfing, investigators excluded visits from participants who reported using only daily PrEP because PrEP surfing would provide no additional prevention benefit for those consistently using daily PrEP. This left 1,779 visits from 562 participants who used event-driven PrEP or no PrEP. The investigators assessed determinants of PrEP surfing with logistic regression and determinants of intention with linear regression. Standard errors were adjusted for repeated observations from the same participants.
At baseline, participants had a median age of 45 years and reported a median of four sex partners during the previous 6 months. Half reported condomless anal sex with a casual partner, and 37% were PrEP eligible in the preceding 6 months. Overall, 42% had used PrEP, of whom 38% used daily PrEP, 47% used event-driven PrEP and 16% used both regimens.
Factors associated with PrEP surfing
Recent PrEP surfing was reported during 449 of 1,779 visits, or 25%, and 238 of the 562 participants, or 42%, reported PrEP surfing at least once during the study period.
Several characteristics were independently associated with PrEP surfing. Compared with participants reporting 0 to 2 sex partners during the previous 6 months, those reporting 3 to 8 partners had approximately four times the odds of PrEP surfing, as did those reporting 9 or more partners. Recent PrEP use was associated with approximately 3 times the odds of PrEP surfing, while a recent rectal sexually transmitted infection or infectious syphilis diagnosis and an intermediate or high perceived probability of acquiring HIV were each associated with approximately 1.5 times the odds. Participants without a steady partner also had approximately 1.5 times the odds of reporting recent PrEP surfing.
Age was inversely associated with PrEP surfing. Participants aged 45 to 54 years and those aged 55 years or older each had approximately half the odds of reporting PrEP surfing compared with participants aged 16 to 34 years. Participants born outside the Netherlands also had lower odds of reporting PrEP surfing.
Intention predicts PrEP surfing
Investigators also evaluated intention to practice PrEP surfing during the following 6 months using a 7-point Likert scale. High intention, defined as a score of 6 or 7, was reported during 588 of 2,187 visits, or 27%. Nearly half of participants reported high intention during at least one study visit.
Higher intention was associated with condomless anal sex with casual partners, recent PrEP use, not having a steady partner, greater perceived probability of acquiring HIV and greater worry about acquiring HIV. Participants aged 45 years or older reported lower intention than those aged 16 to 34 years. The number of sex partners was not associated with intention for PrEP surfing, but an interaction between the number of sex partners and PrEP use was observed.
Intention also predicted subsequent behavior. Among 1,217 follow-up visits from 475 participants using event-driven or no PrEP, each 1-point increase in intention on the 7-point scale was associated with approximately 1.6 times the odds of reporting PrEP surfing during the subsequent 6 months. The investigators noted that the effectiveness of PrEP surfing for preventing HIV acquisition remains unknown. Its effectiveness depends in part on a sex partner using PrEP as prescribed and reliably disclosing that use. The investigators stated that PrEP surfing should not be recommended as an HIV prevention strategy because its effectiveness depends on the quality of a sex partner’s PrEP-use disclosure and should be strongly discouraged when that use is uncertain.
Study limitations
The study had several limitations. The cohort consisted predominantly of middle-aged men who have sex with men (MSM) with college-level education, while other populations at increased risk of HIV acquisition were underrepresented, limiting generalizability. Investigators assessed whether participants had practiced PrEP surfing during the previous 6 months but not how frequently they did so. In addition, imputation of HIV perception variables might have affected the findings.
The authors concluded that PrEP surfing was practiced by MSM without HIV who did not use PrEP on a daily regimen in and around Amsterdam. “Research on the effectiveness of PrEP surfing is crucial to optimize counselling on PrEP surfing,” they wrote.
Expert commentary
Matt Gravett, MD, MSPH, FIDSA, assistant professor of medicine in the Division of Infectious Diseases at the UAB Heersink School of Medicine, who was not involved in the study, provided IDSA Reporter with commentary on the findings.
“I think that this study shows us the ingenuity of community members who are knowledgeable about PrEP yet do not or cannot use PrEP,” Dr. Gravett said. “While it’s a relatively novel approach, it does partly remind us of treatment as prevention wherein a person can rely on their sex partner as a means to protecting themselves from HIV. A key component of this strategy would be open, honest dialogue between partners that enables a person to make an informed decision about their own sexual health. These data show us that this is a phenomenon that’s already occurring, so more research is needed to understand not only why but also the effectiveness of this approach.”
The authors reported having no relevant conflicts. The Amsterdam Cohort Studies is part of the Netherlands HIV Monitoring Foundation and receives financial support from the Center for Infectious Disease Control of the Netherlands National Institute for Public Health and the Environment.
