HIV incidence, sexual and reproductive health among high-risk females recruited for participation in HIV prevention trials in Tanzania

Abstract

Background: Testing and evaluating new HIV prevention products such as HIV vaccines, requires identifying, enrolling and retaining cohorts of HIV high risk individuals. This thesis describes the recruitment and follow up of high-risk females for participation in HIV prevention trials in Tanzania. Specifically, the thesis describes a cohort of female sex workers (FSWs) in Dar es Salaam recruited for participation in an upcoming HIV vaccine trial- known as PrEPVacc vaccine trial, as well as changes in sexual risky behaviours in a similarly high-risk cohort from northern Tanzania.

Methods: Between October and December 2018, FSWs aged 18–45 years were recruited using a Respondent Driven Sampling method. They were screened for eligibility and 700 of them were enrolled into the PrEPVacc registration cohort in Dar es Salaam. At screening and at 3 monthly follow-up visits, social demographics, HIV risk behavioural assessments and collection of blood samples for HIV testing were done. Qualitative interviews were conducted to explore contraceptive use. Data from a separate cohort of high-risk women from Northern Tanzania was used to explore changes in sexual behaviour and its association with HIV incidence.

Results: The baseline HIV prevalence in the PrEPVacc registration cohort was 7.6% (59/773, 95% CI; 5.8%-9.7%). There were 21 HIV seroconversions over a 12 month follow up period. The HIV incidence rate was 3.45 per 100 person-years-at-risk (PYR) (95% CI; 2.25-5.28/100 PYR). The HIV incidence rate was higher among FSWs aged 18-24 years (4.31/100PYR), those using illicit drugs (4.25/100PYR) and those diagnosed with either Syphilis or Hepatitis B/C virus (10.04/100 PYR). (Study I). Nearly half (49%) of high-risk women enrolled in the cohorts from northern Tanzania did not change their sexual behaviour practices after 12 months, while 25% had higher risk practices after 12 months of follow up. The proportion of women reporting multiple partners, transactional sex and high-risk sex practices declined at each 3 months visit (33%, 43% and 47% reduction in odds per visit respectively, p for linear trend <0.001 for all). There was no evidence of an effect of change in sexual behaviour on HIV rate after adjusting for other factors (adjusted odds ratio (aOR) 0.88 95%CI 0.39-2.01, P=0.76) (Study II). In the PrEPVacc registration cohort, awareness of HIV pre-exposure prophylaxis (PrEP) increased from 67% at cohort enrolment to 97% after 12 months (p<0.001). Willingness to use PrEP was high at both time points (98% vs 96% p=0.84). Only 8% (57/700) of the FSWs reported to have ever initiated PrEP use over the 12 months follow-up period. Use of PrEP was independently associated with: marital status i.e married/cohabiting (aOR) 4.19; 95%CI 1.44-12.18) or separated/divorced/widowed (aOR 2.38; 95%CI 1.17-4.83) and engaging in sex with a HIV infected partner (aOR 3.98;1.20-13.15) (Study III). FSWs in the PrEPVacc registration cohort reported that sex work impedes good contraceptive behaviour because; FSWs felt unable to negotiate consistent condom use, avoided health services due to stigma, missed monthly contraceptive supplies because of inconvenient clinic operating hours and skipped contraceptive pills when intoxicated after taking alcohol. Financial hardships related to child rearing and painful abortion experiences influenced FSWs’ commitment to good contraceptive behaviour (Study IV).

Conclusions: The high HIV incidence among FSWs in the PrEPVacc registration cohort demonstrates that this population is suitable for participation in HIV vaccine trials. The HIV incidence may decline over time because of reduction in sexual risky behaviour practices and increased PrEP uptake.