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Reported cases of Lyme disease have more than doubled since 1991, when Lyme became a nationally notifiable disease, according to a report by the Centers for Disease Control and Prevention (CDC). The report also said 93 percent of reported cases were concentrated in 10 states.
"This increase in cases is most likely the result of both a true increase in the frequency of the disease as well as better recognition and reporting due to enhanced detection of cases," said Dr. Paul Mead, a medical epidemiologist with the CDC Division of Vector-Borne Infectious Diseases.
Lyme disease is the most common of all the diseases in the United States transmitted by mosquitoes, ticks and fleas, with approximately 20,000 cases reported each year. It most commonly occurs in the Northeastern, Mid-Atlantic, and North-Central states. Connecticut, Delaware, Maryland, Massachusetts, Minnesota, New Jersey, New York, Pennsylvania, Rhode Island and Wisconsin had the most cases. The report says that during 2003-2005, a total of 64,382 Lyme disease cases were reported to CDC from 46 states and the District of Columbia.
In 1991 fewer than 10,000 cases of Lyme disease were reported.
Most illnesses occurred in June, July and August, when the infected ticks that carry the disease are most active. Lyme disease is caused by the spirochete Borrelia burgdorferi which is transmitted to humans by tick bite.
From 2003 to 2005, the incidence of Lyme disease in the cases reported higher rates among two age groups-children aged 5 to 14 years (10 cases per 100,000 population per year) and adults aged 55 to 64 years (9.9 cases per 100,000 population per year).
Early symptoms of infection include fever, headache, fatigue, and a characteristic skin rash called erythema migrans. Left untreated, infection can spread to joints, the heart, and the nervous system.
People should watch for symptoms especially in these areas with intense Lyme disease transmission, and see a health care provider if these develop. Prompt diagnosis and treatment are important to prevent serious illness and long-term complications.
"While this increase is of concern, these rates highlight the need to focus on prevention of this disease. People living in areas where Lyme disease is most frequently reported can take proactive steps to reduce their risk of infection," Mead said.
Prevention steps include daily tick checks (self examination for ticks), use of repellent containing 20 percent or more DEET, selective use of insecticides that target ticks, and the avoidance of tick-infested areas. Removing ticks within 24 hours of attachment greatly reduces the likelihood of disease transmission. Tick populations around homes and in recreational areas can be reduced 50 to 90 percent through simple landscaping practices such as removing brush and leaf litter, and creating a buffer zone of wood chips or gravel between forest and lawn or recreational areas.
The full report, "Lyme Disease - United States, 2003-2005," is available online at www.cdc.gov/mmwr.