Epidemiology of Colorado tick fever in Montana, Utah, and Wyoming, 1995-2003.

Abstract Colorado tick fever (CTF) is a biphasic, febrile illness caused by a Coltivirus and transmitted by the Rocky Mountain wood tick, Dermacentor andersoni, in the western United States and Canada. Symptoms generally include acute onset of fever, headache, chills, and myalgias; illness often lasts for 3 weeks or more. Laboratory-confirmed cases of CTF were identified from public health department records in Montana, Utah, and Wyoming, and from the Centers for Disease Control and Prevention diagnostic laboratory records. Additional descriptive epidemiologic data were obtained by medical record abstraction. Ninety-one cases were identified from 1995 to 2003, resulting in an overall annual incidence of 2.7 per 1,000,000 population. The annual incidence decreased over the 9-year study period. Cases were 2.5 times more frequent in males than females. The highest incidence of cases occurred in persons aged 51–70. Tick exposure prior to illness onset was reported in 90% of the cases in which a more detailed ...