Lyme disease trends--Dutchess County, New York, 1992-2000.

Background: Lyme disease is a vector-borne infectious disease, accounting for more than 95% of all reported vector-borne illness in the United States. From 1992-2000, Dutchess County reported more cases of Lyme disease than any other county in the United States, consistently ranking among the top ten in incidence rates. We analyzed 1992-2000 Dutchess County Lyme disease surveillance data to characterize Lyme disease trends, identify high-risk populations, and examine the frequency of the characteristic lesion, erythema migrans. Methods: A Lyme disease case was defined as a person with physician-diagnosed erythema migrans or at least one "late" manifestation of the disease, with laboratory confirmation. A surveillance database of cases reported in Dutchess County from 1992-2000 was obtained from the New York State Department of Health. Annual incidence rates by age, gender, race, ethnicity, and ZIP codes, and frequency of erythema migrans were calculated. Results: From 1992 through 2000, a total of 9,548 cases of Lyme disease were reported by Dutchess County to the New York State Department of Health, for a crude mean annual incidence rate of 400 cases per 100,000 persons per year. The incidence rate peaked at 683/100,000 in 1996, and then declined from 1998 to 2000. A bimodal age distribution was seen, with the initial peak among children aged 5-9 years (617/100,000) and the second peak among adults aged 60-64 years (627/100,000). A male preponderance was clearly seen between the ages of 5-19 years, and beyond the age of 60 years. Highest incidence rates were reported in central Dutchess County. Onset of illness occurred most frequently in June, July, and August. Ninety-four percent of cases occurred among the predominantly white population, which had the highest incidence rate (431/100,000) among the races. Incidence rate for non-Hispanics was more than double that for Hispanics. Eighty-one percent of reported cases had erythema migrans. Conclusions: While some prevention programs could be broadly targeted to the entire Dutchess County population, other interventions might be most effective if they focused on the high-risk population groups and areas defined in this report. The high proportion of cases with erythema migrans suggests that early diagnosis and treatment should be effective in reducing late-stage complications of Lyme disease in Dutchess County. Surveillance data for other endemic counties and states can be similarly analyzed to enhance and monitor local prevention programs.