This disease is limited to the western US and is most prevalent from March to September, with the highest numbers of infections occurring in May and June.
Symptoms start about 3 to 6 days after the tick bite. Symptoms of fever continue for 3 days, stop, then recur 1 to 3 days later for another few days.
Risk factors are recent outdoor activity and recent tick bite. The incidence is high in Colorado, where up to 15% of regular campers show past exposure (based on antibodies). It is much less common in the rest of the US.
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