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.