Long-lasting insecticidal nets in Zambia: a cross-sectional analysis of net integrity and insecticide content

BACKGROUND: Long-lasting insecticidal nets (LLINs) are a mainstay of malaria prevention in Africa. More LLINs are available now than in any time previously due to increases in funding for malaria control. LLINs are expected to last three to five years before they need to be replaced. Reports of nets lasting less than three years are frequent in Zambia, which, if true, will increase the number of LLINs needed to maintain universal coverage. METHODS: This study collected nets distributed during mass distribution campaigns. One net was collected from each participating home in 12 districts in 2010 and all nets were examined for holes. One household member was surveyed about net use and care. RESULTS: The study collected 713 polyester nets with a median age of 31 months (range 27–44 months, interquartile (IQR) range: 29–36 months), median number of holes was 17 (IQR: 5–33), and median total hole size was 88.3 sq cm (IQR: 14.5-360.4). The median total number of holes did differ by age of the net, from 27–44 months, but not in a linear fashion. The difference in the number of holes in the newest and oldest nets was not statistically significant. The mean deltamethrin level for all nets was 23 mg/sq m (≥8 mg/sq m is considered effective). There was a larger total hole area in the lower half of the nets (repeat measures ANOVA, F = 228.43, df = 2, p < 0.0001) compared to the upper half and roof of the net. Only 8.7 % of nets had evidence of repairs. CONCLUSIONS: At 27 − 30 months, LLINs already had a large total hole surface area that was equivalent to the oldest nets observed. Nets were often tucked under reed mats which may explain the finding that the largest hole area was found in the lower half of the net. Studies need to be conducted prospectively to determine when physical deterioration occurs and why nets are discarded. Re-enforcing the lower half of the sides of LLINs may help decrease holes.