BACKGROUND: Tularemia is a bacterial zoonosis caused by Francisella tularensis. Persons working outdoors are at increased exposure risk during an epizootic. During July 2015, F. tularensis-infected rodents were identified within Devils Tower National Monument (DETO), and a DETO employee developed tularemia. We investigated to assess frequency of F. tularensis exposure, risk factors for exposure, and protective measure use among DETO employees and develop control recommendations.
METHODS: We administered a written questionnaire to DETO employees assessing tick contact, job activities, and protective measure use during the prior 3 months, and conducted a serosurvey; seropositivity was defined as a single antibody titer ≥1:128. We examined differences between seropositive and seronegative employees in frequencies of tick contact (Mann-Whitney U test), job-related activities, and protective measure use (Fisher’s exact test).
RESULTS: Among 44 total DETO employees, 23 (52%) participated in both the questionnaire and serosurvey. Three of 23 employees (13%) were seropositive, indicating prior F. tularensis exposure. Seropositive employees reported contact with a median of 30 ticks (range: 25–35), compared with 6 ticks (range: 0–25) among seronegative employees (P = .008). More seropositive employees used powered blowers (67% versus 5%, P = .034) and collected animal carcasses (100% versus 30%, P = .047) than seronegative employees. Among both seropositive and seronegative employees, 0% always wore insect/tick repellent or always wore a mask during landscaping activities.
CONCLUSIONS: Tick contact and landscaping activities were associated with F. tularensis exposure among DETO employees. There was no association between protective measure use and seropositivity, likely because use was inconsistent among all employees. Persons working outdoors should consistently take measures to prevent exposure during a F. tularensis epizootic.