Relapsing fever Borrelia in California: a pilot serological study

Borrelia spirochetes are tick-borne Gram-negative bacteria that cause disease in humans and animals. Although many studies have focused on Borrelia burgdorferi (Bb), the agent of Lyme disease, recent studies have examined the role of Relapsing Fever Borrelia (RFB) in human disease. In this pilot study, we have evaluated serological reactivity against Bb and RFB in patients residing in California.

Serological testing for reactivity to Bb and RFB antigens was performed in 543 patients with suspected tick-borne illness using a Western blot technique. Further evaluation of a subset of 321 patients residing in California was obtained. Serum samples were tested for IgM and IgG antibodies reactive with Bb and RFB, and samples were classified by county of residence according to Bb reactivity alone, RFB reactivity alone, and dual reactivity against Bb and RFB. Seroreactivity was ranked in counties with the highest absolute number and the highest prevalence of positive samples.

Of the 543 total serum samples, 32% were positive for Bb, 22% were positive for RFB, and 7% were positive for both Bb and RFB. Of the 321 serum samples from patients residing in California, 33% were positive for Bb, 27% were positive for RFB, and 11% were positive for both Bb and RFB. In the California cohort, the highest rates of positive serological testing for Bb were found in Santa Clara, Alameda, and Contra Costa counties, while the highest rates of positive serological testing for RFB were found in Santa Clara, Alameda, Marin, and San Francisco counties. The highest rates of dual reactivity against Bb and RFB were found in Contra Costa, Alameda, and San Francisco counties. Among the 24 counties with patients who were tested, Bb seropositivity alone was found in four counties, RFB seropositivity alone was found in two counties, and seropositivity for both Bb and RFB was found in 14 counties.

Results of this pilot study suggest that seroreactivity against Bb and RFB is widespread in California, and dual exposure to Bb and RFB may complicate the diagnosis of tick-borne disease. Greater awareness of RFB and broader screening for this tick-borne infection is warranted.