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Permethrin-treated underwear led to long-term resistance in body lice
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Permethrin-treated underwear was more efficient than placebo in eliminating body lice in the short term, but led to increased permethrin resistance in the insects collected among homeless people, according to recent study results.
Researchers conducted a double blind, placebo-controlled trial in February and December 2011 of two homeless shelters in Marseille, France. Seventy-three residents (mean age, 56.9 years; 96% men) were selected for the study based on the presence of live body lice. Participants were randomly assigned 0.4% permethrin-impregnated underwear (n=40) or identical placebo (n=33) for 45 days.
During follow-ups on days 14 and 45, data were collected on the presence of live body lice. The proportions of participants free of body lice on days 14 and 45 were the primary and secondary endpoints, respectively.
In the intent-to-treat (ITT) population, 11 participants receiving the permethrin-treated product (28%) were free of live body lice on day 14, compared with three people in the placebo cohort (9%; P=.04); the between-group difference was 18.4 percentage points (95% CI, 1.4-35.4). In the per-protocol population, the proportion also was significantly greater in the permethrin-treated group (34% vs. 11%; P=.03); the between-group difference was 23.7 percentage points (95% CI, 3.6-43.7).
The difference at the secondary endpoint, however, was not sustained in the ITT population: 11 permethrin participants (28%) and nine placebo persons (27%) were rid of live body lice for a between-group difference of 0.2 percentage points (95% CI, –20.3 to 20.8).
The permethrin-treated group had a prevalence of permethrin-resistant haplotype of 51% vs. 44% among placebo participants at day 1, while at day 45 the permethrin cohort showed resistance of 73% vs. 45% (P<.001).
“This trial clearly demonstrates that the use of permethrin-impregnated underwear had the consequence of increasing the percentage of permethrin-resistant body lice in sheltered homeless persons,” the researchers concluded. “These findings lead us to recommend avoiding the use of permethrin to treat body lice infestations, although implementing new strategies is crucial.”
Disclosure: The researchers report no relevant financial disclosures.
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