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

Introduction: Diarrhoea 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.