Probable: any other case of physician-diagnosed Lyme disease that has laboratory evidence of infection (as defined above). Suspected: a) a case of EM where there is no known exposure (as defined below) and no laboratory evidence of infection (as defined above), or b) a case with laboratory evidence of infection but no clinical information available (e.g. a laboratory report). Lyme disease reports will not be considered cases if the medical provider specifically states this is not a case of Lyme disease, or the only symptom listed is "tick bite" or "insect bite." Comments The surveillance case definition was developed for national reporting of Lyme disease; it is not intended to be used in clinical diagnosis. Definitions of terms used in the clinical description and case definition sections are listed below. Erythema migrans (EM) For purposes of surveillance, EM is a skin lesion that typically begins as a red macule or papule and expands over a period of days to weeks to form a large round lesion, often with partial central clearing. A single primary lesion must reach 5 cm in size. Secondary lesions may also occur. Annular erythematous lesions occurring within several hours of a tick bite represent hypersensitivity reactions and do not qualify as EM. For most patients, the expanding EM lesion is accompanied by other acute symptoms, particularly fatigue, fever, headache, mildly stiff neck, arthralgia or myalgia. These symptoms are typically intermittent. The diagnosis of EM must be made by a physician. Laboratory confirmation is recommended for persons with no known exposure, but with compatible symptoms.