CDC Expands Lyme Disease Guidance to Emerging States

Lyme disease is no longer confined to traditionally high-incidence regions. As case numbers rise in neighboring states, the CDC now advises clinicians to consider Lyme disease beyond historically endemic areas.

Previously, the CDC focused on 14 high-incidence states in the Northeast, mid-Atlantic, and upper Midwest. These included Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia, and Wisconsin.

Lyme Disease Increasing in Neighboring States

That approach is changing. The CDC now recommends considering Lyme disease in states where incidence is increasing.

“The majority (eight of 11) of neighboring states displayed an overall increasing trend in the number of confirmed cases reported,” write Schwartz and colleagues.

These neighboring regions include the District of Columbia and 11 states: Illinois, Indiana, Iowa, Kentucky, Michigan, North Carolina, North Dakota, Ohio, South Dakota, Tennessee, and West Virginia.

Key Findings from CDC Surveillance Data

The MMWR report highlights several clinical patterns:

Carditis and neurologic symptoms were relatively consistent but peaked among patients aged 50–55 years
Carditis disproportionately affected patients aged 20–40 years
Erythema migrans was least frequently reported in patients aged 10–14 years
Arthritis was most common in patients aged 10–14 years
Black patients comprised a higher proportion of cases with carditis compared with overall case distribution
During winter months (December–March), arthritis was the most common presentation

Limits of Surveillance Definitions

A 2017 change in the definition of a confirmed Lyme disease case may underestimate the number of infections outside high-incidence states.

In lower-incidence regions, laboratory confirmation is often required for diagnosis. This can lead to under-recognition, particularly early in illness when testing may be negative.

For more on testing limitations, see Lyme disease testing and diagnosis.

Clinical Judgment Matters

The CDC now emphasizes that clinical suspicion should not be limited by geographic classification.

“A diagnosis of Lyme disease should be considered in patients with compatible clinical signs and a history of potential exposure to infected ticks,” the authors explain, “not only in states with high incidence but also in areas where Lyme disease is known to be emerging.”

This shift reflects a broader understanding that Lyme disease risk is expanding and that surveillance categories may lag behind real-world patterns.

For a clinical overview of presentations, see the Lyme disease symptoms guide.

Clinical Takeaway

Lyme disease is increasing in emerging states. Clinicians should rely on clinical judgment—considering symptoms and exposure risk—even outside traditionally high-incidence regions.

High prevalence of Babesia microti in Suffolk County, New York
Tick-borne co-infections are the norm, not the exception

Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

Symptoms • Testing • Coinfections • Recovery • Pediatric • Prevention