Health Advice



Why confirmed cases of Lyme disease have increased

Deb Balzer, Mayo Clinic News Network on

Published in Health & Fitness

Recent tracking rule changes led to a significant increase in reported Lyme disease cases in the U.S.

The Council of State and Territorial Epidemiologists and the Centers for Disease Control and Prevention updated definitions to better understand the tick-borne disease. In 2022, reported cases rose by 68.5% after the new definition went into effect.

"The new Lyme disease case definition allows us to get a more accurate count of Lyme disease cases in high-incidence areas, which will improve our understanding of Lyme disease and its impact on people living in the United States," says Dr. Bobbi Pritt, director of the Clinical Parasitology Laboratory at Mayo Clinic.

Lyme disease is a bacterial infection caused by the bite of an infected black-legged tick, commonly known as a deer tick.

It is most common in the Upper Midwest and the Northeast and mid-Atlantic states. And it's also common in Europe, Asia, and in south-central and southeastern Canada.



Patients may present with a rash at the site of the tick bite — classically with a bull's-eye rash. But that's not always the case.

"Also, some people may have a rash and not know if it's on the back of their head or another hard-to-see and hard-to-reach area. If the infection is not treated right away, the patient may then progress to having other symptoms, like disseminated rashes, joint pain, arthritis and even neurologic involvement. And they can even have one-sided facial paralysis, called Bell's palsy," says Dr. Pritt.

Lab tests help confirm or rule out diagnoses of Lyme disease. Dr. Pritt says that Mayo Clinic Laboratories perform more than 300,000 tests for tick-borne diseases each year.

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