Clinical manifestations of Lyme borreliosis, serology and exposure to ticks among tick bite cases with evidence of <i>Borrelia</i> infection within three months after a tick bite.

EM = erythema migrans; n.a. = no tick available for testing. *C6 ELISA test results were scored as negative (ELISA index score, <0.90), borderline (0.90 to 1.09), or positive (≥1.10). **Seroconversion of IgM and/or IgG in the immunoblot and/or in the C6 ELISA was considered as evidence of an early Borrelia infection. For seroconversion in the C6 ELISA, the ELISA index score was required to be <1.10 in the baseline serum, and ≥1.10 in the consecutive serum, with a minimum increase of 1.5 points. ‡case #15 was excluded from risk analyses, as the development of Lyme borreliosis was almost certainly not attributable to the tick bite at baseline.