A study protocol for a multi-arm, parallel group randomized-controlled trial evaluating the individual and combined effects of behavioural promotion and hardware provision on handwashing with soap in peri-urban Lusaka, Zambia.

IntroductionDiarrhoea and lower respiratory infections remain leading causes of under-five mortality in sub-Saharan Africa. Handwashing with soap (HWWS) is a cost-effective intervention, yet adherence remains low. Effective interventions must address multiple behavioural influences, as knowledge alone is insufficient without supportive environments. Multi-component handwashing interventions target diverse behavioural determinants, yet few studies isolate the individual and combined effects of different components. This multi-arm randomised-controlled trial in Lusaka, Zambia, aims to assess the individual and combined effects of hand hygiene behavioural promotion and handwashing hardware and supply provision on HWWS at handwashing opportunities, strengthening the evidence base for designing sustainable handwashing interventions. Methods and analysisThis superiority, multi-arm, parallel group randomised-controlled trial will be conducted in five peri-urban communities in Lusaka, Zambia, with 1800 households randomly assigned to four arms (450 households per arm) (1:1:1:1): (A) Handwashing hardware and supply provision only, (B) Hand hygiene behavioural promotion only, (AB) Hand hygiene behavioural promotion + hardware and supply provision, (C) control (no intervention). Households receiving the hardware and supply intervention (A, AB) will receive a handwashing facility and supplies to make liquid soap solution with a maintenance check after three-months. Households receiving the hand hygiene behavioural promotion intervention (B, AB) will receive five bi-weekly visits with a sixth follow-up visit four weeks later. HWWS behaviour of one household member will be assessed through structured observations at baseline and endline (6-months after intervention delivery begins). Ethics and disseminationEthical approval was obtained from London School of Hygiene and Tropical Medicine, Research Ethics Committee, London, UK (Ref: 31387), the University of Zambia Biomedical Research Ethics Committee (Ref: UNZABREC 5834-2024) and the Zambia National Health Research Authority (NHRA-1823/23/12/2024). Results of the main trial will be submitted for publication in a peer-reviewed journal. Trial Registration NumberNCT06865495; ClinicalTrials.gov; Pre-results; Initial release date 04-Mar-2025 STRENGTHS AND LIMITATIONSO_LIThe study provides an opportunity to directly assess the individual and combined impact of handwashing hardware and supply provision and behavioural promotion on handwashing with soap, which can inform future hand hygiene promotion programmes. C_LIO_LIThe large study sample and comprehensive outcome measures will provide unique information about the individual and combined effects of intervention components on behaviour and health. C_LIO_LIWhile structured observations have inherent limitations (participants may alter their behaviour when they are aware they are being observed), it remains the gold standard for the measurement of routine behaviours in domestic contexts. C_LIO_LIThe lack of blinding of study participants and limited blinding of assessors collecting data is a limitation to the study design. This is an acknowledged challenge in the behavioural and environmental health research sector. C_LIO_LISince the intervention is implemented at the household level, there is some potential for contamination of the intervention message between households within communities. However, this risk is minimal given the large sampling interval. Contamination will be assessed during endline data collection. C_LI