Colorado Tick Fever: Clinical, Epidemiologic, and Laboratory Aspects of 228 Cases in Colorado in 1973-1974

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Abstract
During 1973 and 1974, cases of Colorado tick fever were sought throughout Colorado; 228 cases were identified. Although 90% of the patients reported exposure to ticks before illness, only 52% were aware of an actual tick bite. Typical symptoms of fever, myalgia and headache were common, but gastrointestinal symptoms were also prominent in 20% of the patients. Twenty percent were hospitalized; no deaths or permanent sequelae were noted. Persistent viremia (.gtoreq. 4 wk) was found in about half of the cases; this finding was not associated with the occurrence of prolonged symptoms (.gtoreq. 3 wk), which were also reported in half of the cases. One patient became reinfected with the virus. Increasing tourism in endemic areas and the frequent occurrence of prolonged or biphasic illnesses provide the potential for patients with Colorado tick fever to seek medical care anywhere in the USA.