Rapid colorimetric field test to determine levels of deltamethrin on PermaNet surfaces: association with mosquito bioactivity.

OBJECTIVE: To evaluate a simple and inexpensive colorimetric test to measure the amount of cyanopyrethroid insecticide residue from filter paper exposed to mosquito net surfaces. METHOD: The net sampling protocol and colorimetric test (NetTest) were evaluated for deltamethrin-impregnated PermaNet 2.0 by comparison with high-performance liquid chromatographic assays and mosquito mortality (WHO Cone Test). CONCLUSION: The observed correlation between the amount of deltamethrin adsorbed onto the filter paper and the entire amount of deltamethrin per unit area of net material was good: 0.967, five assays. The relationship between the surface levels of deltamethrin determined by the colorimetric test and the 'gold standard' mosquito bioassay reveals a relatively accurate field test with a sensitivity of 91.4% and specificity if 85.4% (76 samplings from 19 nets).