High Incidence and Duration of Antibiotic Use Among a Cohort of Men Who Have Sex With Men in Seattle, Washington.

Background: Doxycycline postexposure prophylaxis (doxy-PEP) effectively prevents bacterial sexually transmitted infections (STIs) but may increase antibiotic pressure. Little is known about longitudinal antibiotic use among men who have sex with men (MSM), a key population for doxy-PEP. Methods: We analyzed data from a prospective cohort of MSM in Seattle, Washington, from 2016 to 2018, prior to the introduction of doxy-PEP. Antibiotic use and reason for prescription were self-reported in weekly surveys and extracted from medical records. We characterized antibiotic use across 49 weeks of follow-up, stratified by specific antibiotics of interest and reasons for prescription. Incidence rates (IRs) were calculated for the number of incident events of antibiotic initiation per 100 person-years (PY) at risk. We assessed factors associated with antibiotic initiation using negative binomial regression to estimate adjusted incidence rate ratios (IRRs). Results: Among 140 participants, 68.6% (n = 96) received at least 1 antibiotic during follow-up, resulting in an overall IR of 264.5 events of antibiotic initiation per 100 PY and 1696 total days of antibiotic use. STI treatment was the most common reason for antibiotic initiation (IR, 153.5 events per 100 PY; 462 days); however, treatment for other conditions contributed most to overall days of antibiotic use (IR, 42.6 events per 100 PY; 947 days). An age of 25-39 years (IRR, 1.54 [95% confidence interval {CI}, 1.02-2.32]) and a history of bacterial STIs <12 months prior to enrollment (IRR, 1.81 [95% CI, 1.12-2.93]) were significantly associated with higher incidence of antibiotic initiation. Conclusions: Antibiotic consumption among this population was very high. Our analysis provides a necessary foundation for assessing the potential impacts of doxy-PEP.