Seroreactivity to the C6 Peptide in Borrelia miyamotoi Infections Occurring in the Northeastern United States

Background. There are no US Food and Drug Administration (FDA)-approved diagnostic tests for Borrelia miyamotoi infection, an emerging tick-borne illness in the United States. The purpose of this study was to evaluate whether the FDA-approved C6 peptide enzyme-linked immunosorbent assay (ELISA) currently used to diagnose Lyme disease may potentially serve as a diagnostic test for B. miyamotoi infections. Methods. Serum specimens from 30 patients from the northeastern United States with B. miyamotoi infection established by a polymerase chain reaction assay of a blood specimen were tested using the C6 ELISA. To reduce confounding with Borrelia burgdorferi coinfection, 6 sera were excluded: 3 from patients with a positive Western immunoblot for antibodies to B. burgdorferi and 3 from patients for whom immunoblot testing had not been performed. Results. Twenty-two of 24 (91.7% [95% confidence interval, 73.0%-98.8%]) evaluable B. miyamotoi patients were C6 ELISA reactive, principally on a convalescent-phase serum specimen. C6 ELISA index values were often well above the positive cutoff value of 1.1, exceeding 4 in 11 of the 22 (50.0%) C6 ELISA-reactive patients. Conclusions. Although previously regarded as a highly specific test for Lyme disease, the C6 ELISA is also regularly reactive on convalescent-phase serum samples of patients from the northeastern United States with B. miyamotoi infection.