Use of biometrics to evaluate intervention coverage and contamination in a cluster randomised trial in Zimbabwe

Introduction Low intervention uptake and contamination can dilute effects of cluster randomised trials (CRTs) but can be difficult to assess. We investigated the feasibility of digital fingerprints to assess intervention coverage and contamination in a CRT of community-based integrated HIV and sexual and reproductive health services for youth (CHIEDZA). Methods 24 clusters in Zimbabwe were randomly allocated to intervention/control. In the 12 intervention clusters, services for youth aged 16-24 years were provided in community halls for 30 months. A population-based survey of youth aged 18-24 years (700/cluster) was conducted to ascertain impact on trial outcomes. Digital fingerprints were collected from service attendees and survey participants, and the two datasets were linked to assess intervention coverage at population level in intervention clusters, and contaminaton in control clusters. Multilevel logistic regression estimated the association of walking distance to the community hall with service uptake. Results Between April 2019-March 2022, 36,9991 clients attended the CHIEDZA service and 36,957 (99.9%) used biometric registration. In the survey 13,675/17,682 (77.3%) participants completed biometric registration: 1182 refused, 1235 bypassed registration and 1590 were unable to register. Database linkage showed that 23.1% of registered survey participants in the intervention clusters (coverage), and 3.7% of participants in control clusters (contamination) attended the CHIEDZA service. Sensitivity of self-reported service attendance against biometric registration match was 75.3% (95%CI 73.1-77.5) and specificity was 92.7% (95%CI 92.0-93.4). In intervention clusters, for every 1km increase in walking distance to the community hall, the odds of utilising the CHIEDZA service reduced by 52% (OR: 0.48 95%CI:0.44- 0.54). Conclusion Biometric identification was highly feasible and acceptable in a community setting with low time pressure. In population-based surveys additional technological challenges emerged. Biometrics enabled good estimation of intervention coverage and validated self-reported data. Community services for youth must overcome distance barriers and ensure communication. Trial registration https://clinicaltrials.gov/study/NCT03719521 registered 23 October 2018