Since its original description nearly 25 years ago,¹ Lyme disease has become recognized as an important infectious disease in the United States. The infection, which is caused by the tick-borne spirochete Borrelia burgdorferi, is now endemic in more than 15 states and has been responsible for focal outbreaks in some eastern coastal areas. Lyme borreliosis is also endemic in Europe and Asia, where certain aspects of the disease (erythema migrans, meningopolyneuritis, and acrodermatitis chronica atrophicans) were described in the early and mid-20th century. These syndromes were linked conclusively in 1982 and 1983 with the recovery of a previously unrecognized spirochete . . .