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Jan. 13 (UPI) — Roughly 500,000 people across the United States are diagnosed with Lyme disease each year, according to new estimates released Wednesday by the Centers for Disease Control and Prevention, but researchers raise concern that some people may be misdiagnosed.

This figure is more than 10 times the number of cases reported to the agency based on blood test results each year, and a roughly 40% increase over estimates for the years 2005 through 2010, agency researchers said.

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The difference likely reflects that physicians are diagnosing patients with the tick-borne disease based on symptoms only, without performing tests to confirm, and may be prescribing drugs, including antimicrobials, in error, the researchers said.

“The estimates we report are influenced by the uncertainties of clinical practice, in which patients are often treated presumptively, inevitably resulting in some degree of over-diagnosis and over-treatment,” the researchers wrote.

“In contrast, cases reported through national Lyme disease surveillance meet a standardized case definition and are more likely to represent actual infections,” they said.

Lyme disease is caused by Borrelia burgdorferi parasites transmitted to humans by specific types of ticks. The infection can involve multiple organs and lead to significant health complications, the CDC said.

However, it is treatable with antimicrobial drugs, and most of those infected recover fully, especially those who receive early and appropriate treatment, it said.

The findings of this analysis are based on insurance claims for inpatient, outpatient and prescription services covering more than 25 million privately insured adults 65 years old and younger in the United States.

The analysis focused on claims related to the diagnosis and treatment of Lyme disease submitted between 2010 and 2018, the researchers said.

Among the adults included in the analysis,118,780 were diagnosed with the tick-borne infections, the data showed.

Of these, 81% occurred among residents of 14 high-incidence states in the Northeast, mid-Atlantic, and upper Midwest regions of the United States, while another 8% involved residents of adjoining states, the researchers said.

Over the nine-year period, an average of 205,000 patients were diagnosed and treated for Lyme disease annually, based on the claims filed, according to the researchers.

Using these figures, the researchers estimated that 476,000 people received a diagnosis of Lyme disease each year between 2010 and 2018, up from the 329,000 projected for the years 2005 through 2010, they said.

“The observed increase in Lyme disease diagnoses between these two periods parallels increases in cases reported through surveillance,” the researchers wrote.

“The difference between our estimate and the [roughly] 35,000 cases reported annually through surveillance is a result of the combined effects of under-reporting of infections and over-diagnosis in clinical practice,” they said.