Research Article: Insecticide-Treated Plastic Sheeting for Emergency Malaria Prevention and Shelter among Displaced Populations: An Observational Cohort Study in a Refugee Setting in Sierra Leone

Date Published: August 01, 2012

Publisher: The American Society of Tropical Medicine and Hygiene

Author(s): Matthew Burns, Mark Rowland, Raphael N’Guessan, Ilona Carneiro, Arlyne Beeche, Stefani Sesler Ruiz, Sarian Kamara, Willem Takken, Pierre Carnevale, Richard Allan.


A double-blind phase III malaria prevention trial was conducted in two refugee camps using pre-manufactured insecticide-treated plastic sheeting (ITPS) or untreated polyethylene sheeting (UPS) randomly deployed to defined sectors of each camp. In Largo camp the ITPS or UPS was attached to inner walls and ceilings of shelters, whereas in Tobanda the ITPS or UPS was used to line only the ceiling and roof. In Largo the Plasmodium falciparum incidence rate in children up to 3 years of age who were cleared of parasites and monitored for 8 months was 163/100 person-years under UPS and 63 under ITPS (adjusted odds ratio [AOR] = 0.40, 95% confidence interval [CI] = 0.33–0.47). In Tobanda incidence was 157/100 person-years under UPS and 134 under ITPS (AOR = 0.85, 95% CI = 0.75–0.95). Protective efficacy was 61% under fully lined ITPS and 15% under roof lined ITPS. Anemia rates improved under ITPS in both camps. This novel tool proved to be a convenient, safe, and long-lasting method of malaria control when used as a full shelter lining in an emergency setting.

Partial Text

It has been estimated that up to one in three malaria-related deaths occurs in countries affected by conflict or natural disaster.1 Refugee and internally displaced populations are highly vulnerable to the effects of malaria, especially if migration occurs from areas of low to high transmission and the population is non-immune.2 The two principal methods of malaria vector control are indoor residual spraying (IRS) and insecticide-treated nets (ITNs), and both work well in endemic regions of Africa and South Asia when the infrastructure for timely supply or campaign planning is well established.3–5 During humanitarian crises, the feasibility of such tools is a major concern, given the demands placed on overstretched delivery agencies, operational constraints, the breakdown of social and public health networks, and the types of refugee shelter available. Times of crisis require fit-for-purpose, ready-to-use, readily stockpiled preventive tools that place no extra demands on hard pressed emergency services.6,7 During the last decade public and private sector organizations, under the leadership of the Roll Back Malaria (RBM) Partnership, have recognized the need to work together to bring complementary expertise to the task of identifying and developing vector control tools appropriate to humanitarian crises.7–9 Insecticide-treated polyethylene sheeting (ITPS), is one such tool emerging from this process and is being produced commercially.10 The ITPS is based on the standard polyethylene sheeting that is issued routinely as temporary shelter for people affected by emergencies. During manufacture the pyrethroid insecticide, deltamethrin, is extruded with the polyethylene into three-ply laminated sheets, comprising an inner low-density laminate and two, outer high-density laminates. The insecticide release characteristics enable the deltamethrin to diffuse slowly to the outer surfaces and to become available for pick-up by any insect that lands on the surface. Consequently, ITPS has a dual purpose: to provide shelter but with vector-control potential. Deployment and erection of ITPS is done in the same way as standard tarpaulin shelters. Until now, evaluation of ITPS has been limited to small-scale entomological testing in scientifically controlled environments “entomological platforms” in Asian11 and “experimental huts” in rural African settings.12,13 Before any novel control tool can go forward for recommendation by the World Health Organization (WHO), or be used routinely in humanitarian crises, clear demonstration of impact on malaria morbidity in emergency refugee settings is essential. A phase III field evaluation was therefore conducted to evaluate the impact of ITPS on malaria incidence in young children in an area of intense transmission. Secondary outcomes were associated with the impact of ITPS on anemia and adverse events (user safety). A unique feature of this trial was its setting—a true emergency—in two newly built refugee camps for Liberian refugees displaced to Sierra Leone. The findings offer insight into the effectiveness of ITPS when used in a scenario for which it was purposefully designed.

The trials showed that ITPS has the potential to be an effective tool for community control of malaria in emergencies depending on how the sheeting is used. Where the ITPS was used to cover walls and ceilings, as in Largo camp, the incidence of childhood malaria was reduced considerably. This method of deployment simulates newly erected refugee camps in acute phase emergencies in which polyethylene sheeting is used to form both the roof and walls of shelters. Although it remains unclear at which point during the 9-month establishment of Largo the ITPS started to provide protection, by the time longitudinal monitoring was able to start, the prevalence of malaria in the overall population was significantly reduced in the ITPS sectors relative to UPS sectors. Given the downward trend in malaria incidence from that point onward, it is reasonable to assume that the protection afforded by ITPS extended well beyond the formal 8-month period of longitudinal monitoring. It is conceivable that the difference in parasite prevalence between ITPS and UPS sectors recorded at the start of longitudinal monitoring reflected a difference between populations on admission. There was no other difference between the origin, recruitment, and characteristics of these two groups and we therefore consider it more likely the difference in prevalence was caused by an intervention effect during the construction phase that continued during the subsequent period of longitudinal monitoring. With the benefit of hindsight, prevalence of infection should have been recorded at arrival however this was not feasible when camps were in early development.