Abstract
BackgroundMalaria transmission in Zanzibar has dramatically reduced in recent years but vector control interventions such as long-lasting insecticidal nets (LLIN) must continue to reach malaria elimination. To achieve this, the Zanzibar Malaria Elimination Programme needs actionable evidence of the durability of the LLIN brands distributed. This study compared physical and insecticidal durability of two LLIN brands: Olyset® and PermaNet© 2.0 in two similar districts on the islands of Unguja and Pemba.MethodsThis was a prospective cohort study of representative samples of households from two districts, recruited at baseline 4 months after the mass campaign. All campaign nets in these households were labelled and followed up over a period of 33 months. Primary outcome was the “proportion of nets surviving in serviceable condition” based on attrition and integrity measures and the median survival in years. The outcome for insecticidal durability was determined by bio-assay from sub-samples of campaign nets.ResultsA total of 834 campaign nets (121% of target) from 299 households were included in the study. Definite outcomes could be determined for 86% of the cohort nets in Unguja (PermaNet® 2.0) and 89% in Pemba (Olyset®). After 33 months, physical survival in serviceable condition was 55% in Unguja and 51% in Pemba. Estimated median survival was lower in Pemba at all time points with 2.3–2.7 years compared to 3.1–3.3 yeas in Unguja. Multivariable Cox proportionate hazard models confirmed the difference between brands (p < 0.0001) and identified household net-care attitude (p = 0.007) and folding of hanging nets during the day (p < 0.0001) as significant determinants, in addition to exclusive use of nets by adults (p = 0.03) and use only over a finished bedframe (p = 0.01). Optimal insecticidal effectiveness was 80% or higher for both brands at all time points when both cone bio-assays and tunnel tests were applied.ConclusionsAfter 3 years of follow-up, Olyset® LLIN showed significantly lower physical survival compared to PermaNet® 2.0 LLIN even after adjusting for other variables of net-use environment and net handling. This suggests that the differences were driven by the textile characteristics of the LLIN brands.
Highlights
Malaria transmission in Zanzibar has dramatically reduced in recent years but vector control interventions such as long-lasting insecticidal nets (LLIN) must continue to reach malaria elimination
The prospect of malaria elimination is threatened by emerging resistance of the vectors [3] and importation of malaria from mainland Tanzania [4]
A retrospective durability assessment of Olyset® distributed through mass campaigns between 2009 and 2011, and second, a 3-year prospective study of three LLIN brands, Olyset®, Netprotect® and PermaNet® 2.0 [7]
Summary
Malaria transmission in Zanzibar has dramatically reduced in recent years but vector control interventions such as long-lasting insecticidal nets (LLIN) must continue to reach malaria elimination. This study compared physical and insecticidal durability of two LLIN brands: O lyset® and PermaNet© 2.0 in two similar districts on the islands of Unguja and Pemba. A retrospective durability assessment of Olyset® distributed through mass campaigns between 2009 and 2011, and second, a 3-year prospective study of three LLIN brands, Olyset®, Netprotect® and PermaNet® 2.0 [7]. Findings from the retrospective study suggested that median survival of Olyset® in mainland Tanzania might be below the assumed 3-year level [8] This was confirmed in the prospective study where median survival estimates of 2.0 years were calculated for Olyset®, 2.5 years for PermaNet® 2.0 and 2.6 years for Netprotect® [9]
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