Specimen collection and processing
PROSTATE
For this sub-study, lateral vaginal wall swab samples were collected between June and December 2017 for STI diagnosis and prostate specific antigen (PSA), a biomarker of semen, testing. Specimens were collected at three timepoints—at baseline (immediately before contraceptive method initiation), month one (M1), and month three (M3). Almost all (96%) participants completed all three visits. Samples were collected by placing Dacron swabs on the lateral vaginal wall and rotating 360 degrees, prior to storage at -80°C for a median time of 23 months (range 21–28 months).Frozen lateral vaginal wall swabs were thawed on ice overnight at 4⁰C prior to elution in 1 mL of phosphate buffered saline (PBS; Sigma-Aldrich, P5493). Tubes were vortexed for 60 seconds and incubated at 4⁰C for 1 hour. Excess mucus was then scraped off the inner wall of the tubes and each tube was vortexed again for 30 seconds.