Field evaluation of Yorkool ®, a long-lasting insecticidal net after 12 months of use in Seme, Kisumu County, Kenya

Background: Physical integrity and insecticidal efficacy of long-lasting insecticide-treated nets (LLINs) is influenced by the handling practices during use. This was an evaluation of Yorkool® pyrethroid-based LLINs after 12 months of use to determine the washing and drying practices, physical conditions and bio-efficacy. Methods: This was a cross-sectional household survey in an area where rectangular Yorkool® a pyrethroid LLINs were distributed during national mass net distribution campaign in 2021. Questionnaires were used for data collection and bioassay tests were done from thirty randomly selected nets. Results: 262 household heads were interviewed with their mean age being 46.9 years (SD 17.4 years) and level of education was mainly primary (70.2%). Most households (71.8%) had 1 to 2 sleeping spaces. The households had a total 468 LLINs with 95.1% having been washed at least once. About three-quarters (74.4%) of the LLINs had been washed using local bar soap, with 99.6 % having not been scrubbed on hard surface during washing and 72.1% were dried under a shade. Those evaluated for physical integrity and had at least one hole made up 77.8% of the nets and 57.2% were too torn and requiring replacement. Bio-efficacy test recorded a mean KD of 92% after 1 hour, and mean mortality of 86% after 24 hours. The nets that passed the WHO efficacy cut off for mortality (≥80%) after 24 hours were 83.3% and 70% passed the KD (≥95%) cut off after 1 hour. Conclusions: While more than a half of the Yorkool® LLINs needed replacement due to poor physical integrity after one year of use in the households, the bio-efficacy of the LLINs was relatively high with the mortality on vectors meeting the WHO threshold