Statistics & Maps
Colorado tick fever (CTF) occurs in people who live in or visit areas where there are infected Dermacentor andersoni ticks. These ticks are found in the western United States or western Canada at elevations of 4,000‒10,000 feet above sea level. Most cases of CTF occur during spring or summer months when ticks are most active. In the United States, a total of 59 CTF cases were reported to CDC from 2010 through 2019. CTF is not a nationally notifiable disease; however, several states require that CTF cases be reported to the state health department. As of September 2020, CTF was specifically reportable in nine states: Arizona, Colorado, Idaho, Montana, New Mexico, Oregon, South Dakota, Utah, and Wyoming. All state health departments are encouraged to report CTF cases to CDC on a voluntary basis.
Approximate geographic distribution of Dermacentor andersoni ticks and counties of residence for confirmed and probable Colorado tick fever virus disease cases, United States, 2010–2019
*All cases were acquired in states where local transmission of Colorado tick fever virus has been reported previously.
**Derived from James AM, Freier JE, Keirans JE, Durden LA, et al. Distribution, seasonality, and hosts of the Rocky Mountain wood tick in the United States. J Med Entomol 2006; 43:17–24.