Misdiagnosis of early Lyme disease as the summer flu.

Lyme disease is often identified by the hallmark erythema migrans rash, but not all early cases present with a rash. In other cases the rash may be unseen or unrecognized by a physician. In these situations, Lyme disease is difficult to diagnose because it masquerades as a non-specific viral-like illness. The seasonal peak of Lyme disease ranging from May through September overlaps with that of viral illnesses such as enteroviral infections, West Nile virus, and in rare years such as 2009, early influenza season. We present a case of a patient with Lyme disease who was initially misdiagnosed with influenza A during the summer of 2009. Because of the diagnostic importance of recognizing the erythema migrans rash, physicians in endemic regions should always ask about new rashes or skin lesions and perform a thorough physical examination when patients present over the summer with viral-like symptoms. Even when no rash is evident, Lyme disease should be considered if these symptoms persist or worsen without a specific diagnosis.