HealthDay News — An estimated 300,000 Americans are diagnosed with Lyme disease each year, but only about 30,000 are reported to the CDC, according to researchers.

This represents a small proportion of the actual disease burden — about a 10th of actual cases. To further complicate matters an unknown number of people are diagnosed with Lyme disease each year who do not actually have it, according to a new report presented at the 2013 International Conference on Lyme Borreliosis and Other Tick-Borne Diseases in Boston.

CDC researchers used data from three ongoing studies, using different methods to estimate the number of people diagnosed with Lyme disease each year. The projects involved analyzing insurance claims information for about 22 million insured people annually for six years, surveying clinical laboratory data and analyzing self-reported Lyme disease cases from a survey of the general public.

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The new preliminary estimate suggests the total number of cases is roughly 10 times higher than the yearly reported number, and supports previous studies that have suggested the true number of cases is between 3- to 12-fold higher than the number of reported cases.

“We know that routine surveillance only gives us part of the picture, and that the true number of illnesses is much greater,” Paul Mead, MD, MPH, chief of epidemiology and surveillance for the CDC’s Lyme disease program said in a statement. “This new preliminary estimate confirms that Lyme disease is a tremendous public health problem in the United States, and clearly highlights the urgent need for prevention.”

The majority of cases reported to the CDC through national surveillance systems are concentrated in the Northeast and upper Midwest regions of the United States, with 96% of cases concentrated in 13 states, and approximately 30% of deer ticks carry the Lyme disease spirochete, according to the CDC.

Lyme disease symptoms include fatigue, headache, mildly stiff neck, joint and muscle aches and fever. If left untreated, the infection can disseminate throughout the body, causing neurologic, cardiac and joint disease for weeks or months.

However, many people do not realize they’ve been infected, as about 20% to 30% of those affected do not develop the characteristic bull’s eye rash, erythema migrans. This makes it essential for clinicians to maintain a high index of suspicion for Lyme disease among patients who present with flu-like symptoms during the summer months.

Encourage patients to wear insect repellent, check for ticks daily and shower within two hours of spending time outdoors, the CDC recommends.

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