Incidence and consequences of damage to insecticide-treated mosquito nets in Kenya

• Published in: Malaria Journal
• Main Authors: Thomas Smith, Adrian Denz, Maurice Ombok, Nabie Bayoh, Hannah Koenker, Nakul Chitnis, Olivier Briet, Joshua Yukich, John E. Gimnig
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2021
• Subjects: Long-lasting insecticidal nets; Malaria; Arctic medicine. Tropical medicine; RC955-962; Infectious and parasitic diseases; RC109-216; Arctic
• Online Access: https://doi.org/10.1186/s12936-021-03978-7; https://doaj.org/article/be4309f5b34c4acbb6db4f04392f60c9

Abstract Background Efforts to improve the impact of long-lasting insecticidal nets (LLINs) should be informed by understanding of the causes of decay in effect. Holes in LLINs have been estimated to account for 7–11% of loss in effect on vectorial capacity for Plasmodium falciparum malaria in an analysis of repeated cross-sectional surveys of LLINs in Kenya. This does not account for the effect of holes as a cause of net attrition or non-use, which cannot be measured using only cross-sectional data. There is a need for estimates of how much these indirect effects of physical damage on use and attrition contribute to decay in effectiveness of LLINs. Methods Use, physical integrity, and survival were assessed in a cohort of 4514 LLINs followed for up to 4 years in Kenya. Flow diagrams were used to illustrate how the status of nets, in terms of categories of use, physical integrity, and attrition, changed between surveys carried out at 6-month intervals. A compartment model defined in terms of ordinary differential equations (ODEs) was used to estimate the transition rates between the categories. Effects of physical damage to LLINs on use and attrition were quantified by simulating counterfactuals in which there was no damage. Results Allowing for the direct effect of holes, the effect on use, and the effect on attrition, 18% of the impact on vectorial capacity was estimated to be lost because of damage. The estimated median lifetime of the LLINs was 2.9 years, but this was extended to 5.7 years in the counterfactual without physical damage. Nets that were in use were more likely to be in a damaged state than unused nets but use made little direct difference to LLIN lifetimes. Damage was reported as the reason for attrition for almost half of attrited nets, but the model estimated that almost all attrited nets had suffered some damage before attrition. Conclusions Full quantification of the effects of damage will require measurement of the supply of new nets and of household stocks of unused nets, and also of ...