Lyme disease is not rare. In the United States, roughly 476,000 people are diagnosed and treated for it each year, making it the most common tick-borne illness in the country. For comparison, the FDA defines a rare disease as one affecting fewer than 200,000 people. Lyme disease exceeds that threshold by more than double annually.
That said, your personal risk depends heavily on where you live. In some parts of the country, Lyme is extremely common. In others, it’s almost unheard of.
The Gap Between Reported and Actual Cases
If you’ve seen statistics saying Lyme disease affects around 30,000 to 40,000 Americans per year, those numbers are outdated and misleading. They come from passive surveillance, meaning only cases formally reported by state health departments to the CDC. In 2023, that number climbed to over 89,000 reported cases, but even that figure drastically undercounts the real burden.
The CDC used insurance claims data covering 2010 to 2018 to arrive at a more realistic estimate: approximately 476,000 people per year receive a Lyme disease diagnosis and treatment. The gap comes from two sources. Many infections are never reported through the surveillance system, which is typical for diseases tracked this way. And many clinicians who diagnose and treat Lyme never record a Lyme-specific billing code in the patient’s chart, so those cases become invisible to anyone counting.
Where Lyme Disease Is Common
Lyme disease clusters in three parts of the United States: the Northeast, the Mid-Atlantic, and the Upper Midwest. A smaller number of cases occur along the Pacific coast, particularly in northern California and southern Oregon. If you live in states like Connecticut, Pennsylvania, New York, New Jersey, Massachusetts, Wisconsin, or Minnesota, Lyme is a routine part of life during warmer months. Your doctor has seen it many times, local pharmacies stock tick removal tools, and public health campaigns are everywhere.
Outside these regions, Lyme genuinely is uncommon. In the South, Southwest, and most of the Western U.S., ticks that carry the bacteria are either absent or far less prevalent. But the map is shifting. Recent data show the geographic footprint of Lyme expanding outward from its northeastern core. States like Michigan, Ohio, West Virginia, Kentucky, and North Carolina are seeing growing signals of Lyme activity that may not yet be fully reflected in official case counts. North Carolina in particular is considered part of the southern leading edge, where the disease is pushing into new territory.
Lyme Disease Outside the U.S.
Lyme is a significant public health concern across much of Europe as well. An estimated 129,000 cases are reported annually across European countries, and underreporting likely means the true number is higher. Western Europe sees roughly 22 cases per 100,000 people per year on average, but some countries far exceed that. Slovenia has recorded incidence rates above 200 per 100,000 people, with a peak of 365 per 100,000 in 2018. Estonia, Lithuania, and Switzerland also consistently report rates above 100 per 100,000.
On the lower end, the United Kingdom reports fewer than 6 cases per 100,000 annually, and Portugal reports fewer than 1 per 100,000. So the pattern mirrors the U.S.: Lyme is common in certain latitudes and ecosystems, and genuinely rare in others.
Why Risk Feels Unpredictable
Even within high-incidence states, your risk varies by neighborhood, lifestyle, and season. Spending time in wooded or grassy areas during late spring and summer puts you in direct contact with the juvenile ticks (nymphs) responsible for most human infections. These nymphs are roughly the size of a poppy seed, easy to miss on skin or clothing. Ticks that stay in suburban lawns bordering wooded areas are just as capable of carrying the bacteria as those deep in forests.
One important detail: an infected tick generally needs to be attached for more than 24 hours before it can transmit the Lyme bacterium. This means finding and removing ticks promptly after outdoor activity substantially lowers your risk, even in areas where infection rates among ticks are high.
Diagnosis Can Be Tricky Early On
Part of the reason Lyme sometimes feels mysterious or “rare” to patients is that early-stage infections are hard to confirm with blood tests. The standard two-step blood testing approach catches fewer than half of early localized infections. A newer version of the test improves that somewhat, but sensitivity in early disease still sits below 70%. Blood tests become highly reliable later, with over 99% sensitivity for late-stage infections, but by then the disease may have progressed.
This means many early Lyme cases are diagnosed based on symptoms and exposure history rather than a definitive lab result. The hallmark bullseye rash appears in a majority of cases but not all, and it can show up in atypical forms or in places that are hard to spot. If you live in or have recently visited a high-risk area and develop flu-like symptoms, joint pain, or an expanding rash in the weeks after a possible tick exposure, that clinical picture matters more than a negative blood test taken too early.
Common, but Unevenly Distributed
Lyme disease sits in an unusual category. It is one of the most frequently diagnosed infectious diseases in the Northern Hemisphere, yet someone living in Arizona or Alabama could go their entire life without encountering it. Whether Lyme is “rare” depends entirely on geography. Nationally and globally, it is far too common to qualify as rare by any medical or regulatory definition. But your individual risk is shaped by the specific patch of ground you walk on, the season you walk on it, and how quickly you check yourself for ticks afterward.