Durable wall lining for malaria control in Liberia: results of a cluster randomized trial.

Background: Malaria control in Liberia depends upon universal coverage with pyrethroid-impregnated long-lasting insecticidal nets (LLINs). Despite regular mass distribution, LLIN coverage and usage is patchy. Pyrethroid resistance in malaria vectors may further reduce LLIN efficacy. Durable Wall Lining (DWL), a novel material treated with two non-pyrethroid class insecticides, was designed to be installed onto the surface of inner walls, and cover openings and ceiling surfaces of rural houses.

Objectives: AIM: To determine the malaria control efficacy of DWL.

Primary Objective: To determine if DWL has an additional protective effect in an area of pyrethroid resistance.

Secondary Objectives: To compare surface bio-availability of insecticides and entomological effectiveness over the study duration.

Design: A cluster randomized trial.

Participants: Children aged 2-59 months.

Control Arm: 50 houses per 20 clusters, all of which received LLIN within the previous 12 months.

Active Arm: 50 houses per 20 experimental clusters, all of which received LLINs with the previous 12 months, and had internal walls and ceilings lined with DWL.

Randomisation: Cluster villages were randomly allocated to control or active arms, and paired on 4 covariates.

Main Outcome Measures: PRIMARY MEASURE: Prevalence of infection with P. falciparum in children aged 2 to 59 months.

Secondary Measure: Surface bioavailability and entomological effectiveness of DWL active ingredients.

Results: Plasmodium falciparum prevalence in active clusters after 12 months was 34.6% compared to 40.1% in control clusters (p = 0.052). The effect varied with elevation and was significant (RR = 1.3, p = 0.022) in 14 pairs of upland villages. It was not significant (RR = 1.3, p = 0.344) in 6 pairs of coastal villages. Pooled risk ratio (RR) was calculated in SAS (Cary, NC, USA) using the Cochran-Mantel-Haenszel (CMH) test for upland and coastal cluster pairs. DWL efficacy was sustained at almost 100% for 12 months.

Conclusions: Findings indicate that DWL is a scalable and effective malaria control intervention in stable transmission areas with pyrethroid-resistant vectors, where LLIN usage is difficult to achieve, and where local housing designs include large gable and eve openings. Trial registration ClinicalTrials.gov identifier: NCT02448745 (19 May 2015): https://clinicaltrials.gov/ct2/show/NCT02448745.