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Lyme Disease Cases Down From Last Year, but Up In General

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March 15, 2001 -- Though the number of cases of Lyme disease in the U.S. decreased slightly in 1999, the number of cases of this tick-borne illness more than doubled during the 1990s, according to the latest government data.

Lyme disease cases decreased by 3% in 1999, compared with 1998, to nearly 16,300 reported cases. However, when the 1999 figures were compared with 1997, there was a 21% increase, according to the data published by the CDC in the March 16 issue of Morbidity and Mortality Weekly Report.

The 1999 data show that most cases were reported in the northeastern, mid-Atlantic and north central states. Nine states -- Connecticut, Rhode Island, New York, Pennsylvania, Delaware, New Jersey, Maryland, Massachusetts, and Wisconsin -- accounted for the lion's share of new cases.

"Although the cases reported in 1999 are fewer than the peak number of cases reported in 1998, the data from the 1990s -- and since the epidemic began -- are showing a trend toward higher numbers," says researcher Stacie Marshall, MPH, an epidemiologist at the CDC's division of vector-borne infectious diseases in Fort Collins, Colo. Vector-borne diseases are passed by ticks, insects, and rodents, and Lyme disease is the most common vector-borne disease.

The reasons for the apparent increase are twofold, she explains. There has been an increase in surveillance efforts, so more cases are being detected, and people are spending more time outdoors in tick-infected areas.

Lyme disease is usually caused by deer ticks that transmit the bacterium Borrelia burgdorferi to humans. A bull's-eye rash is typically the first sign of infection, but a few months after the bite, arthritis may appear as brief bouts of pain and swelling in one or more large joints, especially the knees. Additionally, numbness, pain, Bell's palsy (paralysis of the facial muscles, usually on one side), and meningitis (fever, stiff neck, and severe headache) may occur later in the infection.

But serious consequences can be staved off with early diagnosis and proper antibiotic treatment.

Most people who developed Lyme disease in 1999 were either younger than 15 or between 45 and 59, and cases were mainly reported during June and July, the data show.

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