6 participants received a referral paper with their name and unique ID, which was presented to clinicians from PASADA. Clinicians provided HIV counseling, an explanation of the HIV blood test procedure, and a referral to the clinic lab for testing, where a finger prick sample was taken and processed. The results from the blood test were delivered in a private office after verifying the unique ID and name of each individual. Individuals who tested positive were referred to HIV treatment services available at no charge to patients in Tanzania. Those who were determined to be HIV-negative and met all other eligibility criteria were enrolled in the study by research assistants after providing informed consent. Enrolled participants were also tested for HSV2 and syphilis using fingerstick-based rapid blood tests, and for trichomonas vaginalis using a vaginal swab. Syphilis and trichomonas test results were returned within 30 minutes, and positive syphilis tests were then verified through confirmatory testing; those testing positive for these STIs were offered free treatment.

All non-attriting participants were again tested at endline for the same STIs (HIV, HSV2, syphilis, and trichomonas) using the same testing, counseling, and treatment procedures. The one exception is that participants who tested positive for HSV2 at baseline were not re-tested for HSV2 at endline, since we tested for IgG antibodies that indicate whether the individual has ever been infected with HSV2. In order to verify the accuracy of the HSV2 tests, at endline we compared the results of the OnSite Duo rapid test with an ELISA laboratory test for 30 of the participants, finding 80 percent sensitivity and specificity, which we deemed minimally acceptable.

Baseline and endline surveys were administered in Kiswahili on tablets by research assistants from Innovations for Poverty Action Tanzania. These surveys were conducted in private spaces at the PASADA clinic.

The primary approach used for tracking participants in this unstable FSW study population was via cell phone, with both main and backup numbers requested at enrollment. In late 2019, however, the Tanzanian government required that all cell phones be registered to a national identification card along with biometric confirmation; particularly among those engaged in illegal activity such as FSW, this resulted in many phone numbers being suddenly changed after the government disconnected unregistered phone numbers starting in January 2020. Based on an increase in unsuccessful call attempts, this appeared to significantly contribute to the loss of tracking of our study participants, though we were able to reach a subset of participants at new phone numbers by contacting them through secondary means including via the participant who had originally recruited them. Thus during the COVID-19 pandemic fieldwork hiatus in mid 2020 we attempted to call all 794 lottery-arm participants who had not yet been called for lottery-based random STI testing. However, we were only able to reach 49 percent of this sample, with 36 percent of the phone numbers permanently disconnected. We similarly attempted to contact a randomly selected 55 percent of the control group, and were able to reach 58 percent of them. Others were unable to be reached after three attempts, but this was during a time of extreme pandemic-related disruption;