The potential association between PrEP use and STI incidence is an important public health issue, and better understanding predictors of STI diagnosis among PrEP users is critical to developing companion behavioral support. This analysis presents data from SPARK, a PrEP demonstration/implementation project conducted at a community-based health center in New York City.
Participants were 300 MSM and transgender women (ages 18-63; 48% PoC) patients at the health center who chose to start PrEP. SPARK participants were followed for 12-months and tested quarterly for STIs (urethral/rectal gonorrhea/chlamydia and syphilis). Data were also collected on participants presenting to the health center between study visits for STI testing. Analyses were restricted to the 261 participants (87%) who were retained at 12-months. We examined baseline demographic, behavioral, and psychosocial predictors of STI diagnosis over the 12-month follow-up, as well as change scores (e.g., changes in condom use and number of partners).
11% of participants had an STI diagnosis in the 6 months before starting PrEP. Over the course of 12-month follow-up, 44% of participants were diagnosed with an STI. Diagnoses per visit ranged from 16% (6M) to 10% (12M), and 23% of participants were diagnosed at interim (i.e., non-study) visits to the health center. STI diagnosis was associated with being under 25 (p < .02), but not with race/ethnicity, income, or education. In stepwise regression models including significant bivariate variables, four factors were retained as predictors of STI diagnosis: a) being under 25 (OR = 4.8); b) reporting more than 5 partners at baseline (OR= 3.5); c) STI diagnosis in 6-months prior to PrEP uptake (OR = 3.5); and d) increasing the number of partners from baseline to 12-months (OR=2.1). Average condom use decreased from baseline (60%) to 12-months (45%), but neither overall condom use nor change in condom use were associated with STI diagnosis.
The strength of baseline factors in predicting STI incidence suggests that risk compensation may be less significant than underlying behavior patterns in post-PrEP STI diagnosis. The known association between STI diagnosis and HIV seroconversion suggests that PrEP is effectively preventing new HIV infections. Particular attention and support is needed for younger PrEP users. Although many PrEP prevention messages stress condom use, number of partners appears to be a more important predictor of STI diagnosis among PrEP users.