BACKGROUND: Lyme disease is a multi-system illness caused by the spirochete Borrelia burgdorferiwith over 30,000 cases reported each year to CDC through the National Notifiable Diseases Surveillance System. Over 95% of these cases occur in high-incidence states in the Northeast (Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia) and upper Midwest (Minnesota, Wisconsin). However, cases of Lyme disease have been reported among residents of all 50 states. A retrospective analysis of surveillance cases was performed to explore the epidemiology of Lyme disease in low-incidence states.
METHODS: Probable and confirmed cases of Lyme disease reported during 2005-2009 from four states with a low-incidence of Lyme disease (Florida, South Carolina, Utah and Washington) were reviewed. Variables evaluated included age, sex, travel history, clinical history, and laboratory results.
RESULTS: During 2005-2009, a total of 385 confirmed and probable Lyme disease cases were reported to CDC from the four low-incidence states. Among 297 (77%) patients for whom a travel history was available, 250 (84%) had a history of recent travel to a high-incidence area. Median age was similar for patients with and without travel-related exposure (46 years versus 41 years, respectively). However, the age distribution of patients with travel-related exposure was bi-modal, whereas the age distribution of patients without travel-related exposure was not. Furthermore, 70% of patients without travel-related exposure were female, as compared with 43% of patients with travel-related exposure (p<0.0001). Among 285 patients with both clinical information and travel-history available, erythema migrans rash occurred as frequently in patients without travel-related exposure (31/47, 66%) as those with travel-related exposure (162/238, 68%; p=0.8). The frequency of musculoskeletal and neurologic manifestations did not differ between those without and those with travel-related exposure. The proportion of patients with positive two-tiered testing results was the same (45%) for patients without and those with travel-related exposure.
CONCLUSIONS: Most patients diagnosed with Lyme disease in low-incidence states report travel to high-incidence states. The epidemiology of Lyme disease in low-incidence states among patients who deny any travel-related exposure, however, is distinct from that in high-incidence states. Patients without a history of travel present a diagnostic dilemma; laboratory evidence of infection is important to securing a diagnosis, but the probability that a positive test result represents a true positive infection is lower in low-incidence areas. Accurate diagnosis of Lyme disease in low-incidence areas is essential to providing appropriate care.