Evaluation of the Durability of Long-Lasting Insecticidal Nets in Guatemala

Abstract

Background. Insecticide-treated bednets (ITNs) are widely used for the prevention and control of malaria. In Guatemala, since 2006, ITNs have been distributed free of charge in the highest risk malaria-endemic areas and constitute one of the primary vector control measures in the country. Despite relying on ITNs for almost 15 years, there is a lack of data to inform the timely replacement of ITNs whose effectiveness becomes diminished by routine use. Methods. We assessed the survivorship, physical integrity, insecticide content and bio-efficacy of ITNs through cross-sectional surveys conducted at 18, 24 and 32 months after a 2012 distribution of PermaNet (R) 2.0 in a malaria focus in Guatemala. A total of 988 ITNs were analyzed (290 at 18 months, 349 at 24 months and 349 at 32 months). Results. The functional survivorship of bednets decreased over time, from 92% at 18 months, to 81% at 24 months and 69% at 32 months. Independent of the time of the survey, less than 80% of the bednets that were still present in the household were reported to have been used the night before. Most of the bednets had been washed at least once (88% at 18 months, 92% at 24 months and 96% at 32 months). The proportion of bednets categorized as in ″good condition″ per WHO guidelines of the total hole surface area, diminished from 77% at 18 months to 58% at 32 months. The portion of ITNs with deltamethrin concentration less than 10mg/m2 increased over time (14% at 18 months, 23% at 24 months, and 35% at 32 months). Among the bednets for which bioassays were conducted, the percentage that met WHO criteria for efficacy dropped from 90% at 18 months to 52% at 32 months. Conclusion. While our assessment demonstrated that nets were in relatively good physical condition over time, the combination of declining bio-efficacy over time and low use rates limited the overall effectiveness of the LLINs. Efforts to encourage the community to retain, use, and properly care for the LLINs may improve their impact. Durability assessments should be included in future campaigns.