Unexplained Fever After a Camping Trip in the American Southwest.

An 8-year-old girl was evaluated for fevers of 39.4°C that developed 10 days after returning from a family camping trip. She complained of diffuse headache, nausea, and occasional emesis. Before her illness, 3 transient erythematous papules resembling insect bites on her abdomen were noted. Sore throat, cough, conjunctivitis, diarrhea, arthralgias, and myalgias were absent. Her symptoms, including fever, resolved after 5 days. Five days later, the child presented for outpatient evaluation with new fevers, headache, and nausea. Her review of systems was otherwise negative. Her past medical history was notable for allergic rhinosinusitis, for which she was taking antihistamines. Her immunizations were up to date, and she had no known drug allergies. She resided in a suburb of the San Francisco Bay Area with her parents and younger brother. The family had visited national parks throughout southern Utah and northern Arizona during the spring in the weeks before the onset of illness, where they had hiked and waded into freshwater streams. They stayed in hotels, with the exception of a lodge at Bryce Canyon National Park, and drank only bottled water. There were no indoor or outdoor animal exposures, nor were there ill contacts. There was no history of arthropod bites. Vital signs included a temperature of 38°C, pulse of 104 beats per minute, blood pressure of 110/58 mm Hg, and respirations of 20 per minute. Her physical examination was unremarkable. Electrolytes, liver function tests, and creatinine were normal. The white blood cell count was 12 400/μL with 67% neutrophils (>20% bands), 12% lymphocytes, and 20% monocytes. The hemoglobin was 11.7 (range, 11.5–15.5g/dL) and the platelet count was normal. An erythrocyte sedimentation rate was 90 mm/hour, and the C-reactive protein level was 6.9 mg/dL (range, 0–0.9 mg/dL). A heterophile antibody was positive. Given her recurrent fever, headaches, and history of travel, leptospirosis, tick-borne relapsing fever (TBRF), Colorado tick fever, Epstein-Barr virus, and sequential viral infections were considered. A Giemsa-stained peripheral blood smear is shown in Figure 1.