Which clinical history findings are characteristic of Colorado tick fever?

Updated: Aug 05, 2019
  • Author: Shawn J Sethi, DO; Chief Editor: Jeter (Jay) Pritchard Taylor, III, MD  more...
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Colorado tick fever presents as a nonspecific febrile illness with few historical clues (other than the epidemiology) to suggest the disease. [7] Consider the diagnosis in any patient with a febrile illness who lives in or who recently visited an endemic area. Most patients are males aged 15-45 years who present between April and August. Findings may include a history of tick bite, fever, and flu-like symptoms.

Most patients have a history of tick exposure, but roughly half actually recall tick attachment. Therefore, a history of a tick bite may be a clue, but its absence does not exclude the diagnosis. The patient may also have a history of participation in activities that put him or her at risk for a tick bite.

Fever is present in nearly all cases. A characteristic "saddleback fever" pattern has been noted in about half of cases of Colorado tick fever, which strongly suggests the diagnosis. Patients with this pattern have a fever for 2-3 days, followed by an afebrile period of similar duration and then another 2-3 days of fever.

Common flu-like symptoms include the following:

  • Headache
  • Myalgias
  • Arthralgias
  • Fatigue

In addition, a nonspecific evanescent rash may be present in 5-15% of cases, sometimes with a palatal enanthema. Stiff neck, retro-orbital pain, photophobia [1] , nausea, vomiting, abdominal pain, diarrhea, and sore throat have all been reported in a minority of patients. In one series, patients with suspected Colorado tick fever and symptoms of abdominal pain, rash, or sore throat were less likely to have Colorado tick fever on the basis of serologic diagnoses.

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