Setting: Nairobi is the capital and largest city in Kenya, with a population of approximately 4.4 million people. Nairobi county has an estimated 2032 ‘hot-spots’ where approximately 39,600 women sell sex. Types of hot-spots include bars with lodging (where sex work can take place), bars without lodging, guest houses, streets, sex dens, and uninhabited buildings. Around 73% (29,000) of FSWs in Nairobi are served by seven Sex Worker Outreach Programme (SWOP) clinics which provide peer education and outreach, comprehensive clinical services, including HIV testing and treatment, and condom distribution. Additional programmes provide services for other FSWs.
Sampling and study design: The Maisha Fiti study was designed in consultation with the FSW community in Nairobi, as well as with peer educators and staff working at the seven SWOP clinics. The
study was powered to detect genital inflammation among women who had experienced  recent PSV. Assuming 2:1 exposure to recent violence, enrolling 750 HIV-negative women would detect a 10% absolute difference in the proportion of women who have genital
inflammation (25% vs. 15%) at 90% power. The HIV prevalence among FSWs in Nairobi is approximately 25%, and thus, the target sample size was 1000 FSWs for the study. All women attending SWOP clinics have a unique enrolment number supported
by biometrics (fingerprints). Enrolment numbers were selected from all clinic attendees who had accessed SWOP services in the past 12 months, who were aged 18–45 years, and who did not have an underlying chronic illness (other than HIV) that was likely to
alter host immunology. Of 29,000 FSWs enrolled at one of the seven SWOP clinics across Nairobi, 10,292 met these inclusion criteria and were included in the sampling frame. Additional exclusion criteria (assessed during study enrolment) were current pregnancy or breastfeeding. Of the 10,292 FSWs, 1200 were randomly selected for study participation with numbers weighted by the total population of FSWs enrolled in each SWOP clinic.
Women aged <25 years were oversampled to enable sufficient power for analyses stratified by age. Thus, although <25 year olds represented 11.69% of women meeting the study inclusion criteria, we randomly selected 21.14% to participate in the study (sampling
fraction: <25 year olds 17.6%; 25+ years 8.7%).
Behavioural-biological surveys: These were administered at three time points (baseline, midline, endline). Midline data collection was cut short due to the onset of the COVID-19 pandemic which is why only around one third of women attended the Midline interview. The behavioural survey was administered face-to-face in English or Swahili and contained modules on sociodemographics, adverse childhood experiences, financial stress, violence experience, mental health problems, alcohol and substance use, stigma, and community mobilisation and empowerment. 
Urine samples were collected to test for pregnancy, Chlamydia trachomatis (CT), and Neisseria Gonorrhoea (NG) infection. Blood was taken to test for Treponema pallidum (syphilis). HIV status was screened by rapid HIV tests, with positive tests confirmed using
HIV DNA Genexpert. Self-collected vaginal swabs were used to test for Bacterial Vaginosis (BV; Gram’s stain and Nugent scoring) and Trichomonas vaginalis (TV; OSOM Trichomonas Rapid Test; SEKISUI Diagnostics, Massachusetts, USA). Hair samples were used to test for hair cortisol levels.