Tick-borne relapsing fever in the Pacific Northwest: an underdiagnosed illness?

Some 30 cases of tick-borne relapsing fever due to Borrelia are known to have occurred between 1965 and 1978 in the Pacific Northwest. This disease was found more frequently in young men with a history of wilderness exposure during the summer months. Recurrent fever was the most common symptom with temperatures reaching higher than 39.5 degrees C (103.1 degrees F) in all cases, and many patients had three or more febrile episodes. Splenomegaly was the second most common finding reported. Diagnosis of relapsing fever was made in 20 cases by identifying spirochetes on peripheral blood smears. In ten remaining cases the diagnosis was made on clinical and epidemiologic grounds.Information regarding therapy was available in 21 cases. Ten patients received a tetracycline drug and all had a prompt response without relapse. Two of the patients died, a 68-year-old woman with possible myocardial involvement and a newborn infant with infection acquired in utero and meningeal involvement. The diagnosis was often delayed in spite of outpatient evaluation and admittance to hospital, probably because borreliosis was not considered in the differential diagnosis. Because tick-borne relapsing fever is eventually a self-limited disease in most patients, it is probably not recognized often enough. Awareness of this disease and examination of the peripheral blood smear for spirochetes will lead to earlier diagnosis. Prompt initiation of tetracycline therapy should reduce morbidity associated with borreliosis.