Long-lasting permethrin impregnated uniforms: A randomized-controlled trial for tick bite prevention

Background: Because of frequent exposure to tick habitats, outdoor workers are at high risk for tick-borne diseases. Adherence to National Institute for Occupational Safety and Health-recommended tick bite prevention methods is poor. A factory-based method for permethrin impregnation of clothing that provides long-lasting insecticidal and repellent activity is commercially available, and studies are needed to assess the long-term effectiveness of this clothing under field conditions.

Purpose: To evaluate the protective effectiveness of long-lasting permethrin impregnated uniforms among a cohort of North Carolina outdoor workers.

Design, setting, and participants: A double-blind RCT was conducted between March 2011 and September 2012. Subjects included outdoor workers from North Carolina State Divisions of Forestry, Parks and Recreation, and Wildlife who worked in eastern or central North Carolina. A total of 159 volunteer subjects were randomized, and 127 and 101 subjects completed the first and second years of follow-up, respectively.

Intervention: Uniforms of participants in the treatment group were factory-impregnated with long-lasting permethrin whereas control group uniforms received a sham treatment. Participants continued to engage in their usual tick bite prevention activities.

Main outcome measures: Incidence of work-related tick bites reported on weekly tick bite logs.

Results: Study subjects reported 1,045 work-related tick bites over 5,251 person-weeks of follow-up. The mean number of reported tick bites in the year prior to enrollment was similar for both the treatment and control groups, but markedly different during the study period. In our analysis conducted in 2013, the effectiveness of long-lasting permethrin impregnated uniforms for the prevention of work-related tick bites was 0.82 (95% CI=0.66, 0.91) and 0.34 (95% CI=-0.67, 0.74) for the first and second years of follow-up.

Conclusions: These results indicate that long-lasting permethrin impregnated uniforms are highly effective for at least 1 year in deterring tick bites in the context of typical tick bite prevention measures employed by outdoor workers.