Study protocol for a multi-arm, parallel group randomised controlled trial evaluating the isolated 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 disentangle the isolated and combined effects of different components. This multi-arm randomised-controlled trial in Lusaka, Zambia, aims to assess the isolated and combined effects of hand hygiene behaviour promotion and handwashing hardware and supply provision on HWWS at handwashing opportunities, strengthening the evidence base for designing sustainable handwashing interventions. METHODS AND ANALYSIS: This 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, and (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 3 months. Households receiving the hand hygiene behaviour promotion intervention (B, AB) will receive five bi-weekly visits with a sixth follow-up visit 5 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 DISSEMINATION: Ethical approval was obtained from London School of Hygiene & 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 NUMBER: NCT06865495.