Screening and enrolment
In total 3,828 participants were screened for possible enrolment into observational cohorts before SiVET rollout and 2,622 (69%) were enrolled, figure1. The main reasons for screen failure were non-involvement in sex work (n=612), being at low risk for HIV infection (n=337) and HIV infection (n=215). At the time of introduction of the SiVET protocol, 1,525 (58%) of the participants enrolled into observational cohorts before SiVETs were eligible for screening into SiVETs. The main reasons for ineligibility were having spent more than 18 months in observational cohorts (n=930) and exiting observational cohorts before SiVET protocol roll out (n=121), figure 1. Of the 1,525 eligible for screening, 672 (44%) were consecutively screened and 572 (85%) of these enrolled into SiVETs (282 from FF and 290 from FSW). The main reason for screening but not enrolling into SiVETs was exposure to Hepatitis B (n=52) (assessed as shown in table 1). In total, 953 (283 from FF and 670 from FSW) participants were eligible for follow up in the non-SiVET cohorts in the SiVET concurrent period, figure 1.
Baseline participant characteristics
FF: Compared to non-SiVET1 cohort, SiVET1 cohort had more men 73% vs 48% and more participants aged ≥ 35years, 24% vs 14%, Table 2. Furthermore, non-SiVET1 cohort had more participants without any education 12% vs 6%, working in restaurant/bar/hair salon occupation 23% vs 8% and lived at the current location for one year or less 34% vs 17%, Table 2.
FSW: Compared to the non-SiVET2 cohort, SiVET2 cohort had fewer participants aged ≥ 35 years, 12% vs 22%, Baganda tribe 44% vs 53% and those working in restaurant/bar/hair salon occupation 29% vs 38% Table 2. Additionally, the non-SiVET2 cohort had more participants without any education 41% vs 6%, single never married 36% vs 24% and those that lived at the current location for zero to one year 33% vs 18%, Table 2.
Primary outcome (study dropout)
Among the 1525 participants, 326 (21%) dropped out of the cohorts. Of these 225/953 (24%) dropped out of the non-SiVET cohorts compared to 101/572 (18%), p=0.01 in the SiVET cohorts.
Overall, 326 participants dropped out of cohorts in 1,260 Person Years of Observation (PYO), a dropout rate of 25.9 /100 PYO, 95%CI:23.2-28.8. The dropout rate was higher in the non-SiVET cohorts 31.6, 95%CI: 27.8-36.1 compared to SiVET cohorts 18.4, 95%CI: 15.1-22.4, rate ratio (RR) =0.6, 95%CI: 0.5-0.7, table 3. Stratifying the dropout rate by the study populations, it was still higher in the non-SiVET cohort compared to SiVET cohort in a given population but generally, the dropout rate was highest in the FSW population table 3.
Similarly, comparing dropout rates by similar participant characteristics, the rates were generally higher in non-SiVET cohorts, except for participants that had lived at the current location for zero to one year in the SiVET2 cohort, table 4.
Reasons for dropping out of cohorts
Of the 225 participants that dropped out of non-SiVET cohorts, 89 (40%) were lost to follow up other reasons are shown in figure1. Similarly, of 101 participants that dropped out of the SiVET cohorts, 31 (31%) were lost to follow up, figure 1.
Factors associated with dropout
FF: Factors independently associated with dropout in the non-SiVET1 cohort included sex [female: adjusted rate ratio (aRR) = 0.5, 95%CI: 0.3-0.9)], religion [Muslim: 0.4 (0.2-0.8)], occupation [restaurant/bar/hair salon: 3.1(1.3-7.4) compared to being engaged in small-scale business], other factors are shown in Table 5. In SiVET1 cohort, only duration lived at the current location [> 1 year: 0.5 (0.3-0.9)] was independently associated with dropout.
FSW: Factors independently associated with dropout in the non-SiVET2 cohort included religion [Muslim: 0.6 (0.3-0.9)], marital status [married: 2.2 (1.1-5.6) compared to single never married] and having sex under influence of alcohol [sometimes: 0.4 (0.2-0.8) compared to never]. In SiVET2 cohort, factors independently associated with dropout included age [25-34 years: 0.6 (0.3-0.9), 35 or more years: 0.3 (0.1-0.7) all compared to 18-24 years] and duration lived at the current location [> one year: 0.4 (0.2-0.7)], other factors are shown in Table 5.