Lyme disease is far more common than most people realize. While about 89,000 cases were officially reported to the CDC in 2023, the actual number is dramatically higher. The CDC estimates that roughly 476,000 people are diagnosed and treated for Lyme disease each year in the United States, making it the most common vector-borne illness in the country by a wide margin.
Why the Official Numbers Are So Low
The gap between 89,000 reported cases and 476,000 estimated cases is striking, and it comes down to how disease surveillance works. Not every diagnosis makes it into the reporting system. A doctor in a high-prevalence area might treat dozens of Lyme cases a month and not report each one individually. Some patients are treated based on symptoms and a known tick bite without formal lab confirmation, so they never enter the surveillance database at all.
An analysis of Medicare claims data found that the actual rate of Lyme disease diagnoses was 7.4 times higher than what surveillance picked up during the same period. That ratio held consistently from 2016 to 2019, suggesting this isn’t a one-time fluke but a structural gap in how cases get counted. The true burden of Lyme disease in the U.S. is roughly an order of magnitude larger than the headline numbers suggest.
Where Lyme Disease Is Most Concentrated
Lyme disease is not evenly spread across the country. The vast majority of cases cluster in two regions: the Northeast (from Virginia up through Maine) and the upper Midwest (Minnesota and Wisconsin in particular). These areas have large populations of blacklegged ticks, also called deer ticks, which carry the bacteria that cause the disease. If you live outside these zones, your risk drops substantially, though cases have been documented in nearly every state as tick habitats expand.
The geographic range of Lyme disease has been steadily growing. Warmer winters and shifting wildlife patterns have pushed tick populations into parts of the country where they were once rare, including southern Canada and states bordering the traditional hotspots. Areas that had almost no cases two decades ago are now reporting consistent infections each year.
Peak Season and Timing
April through October is generally the most active tick season, though Lyme disease can be contracted year-round in many parts of the U.S. The highest-risk window falls in late spring and early summer, when nymphal ticks (the juvenile stage) are most active. Nymphs are roughly the size of a poppy seed, which makes them easy to miss on your skin. They’re responsible for the majority of Lyme transmissions precisely because people don’t notice or remove them in time.
Who Gets It Most Often
Lyme disease doesn’t affect all age groups equally. Incidence rates peak in two distinct groups: children ages 5 to 9 and adults between 50 and 79. The childhood peak likely reflects time spent playing outdoors in tick-prone areas. For adults, the highest concentration falls in the 60 to 69 age group (about 21% of cases) and 50 to 59 (about 19%), which may reflect both outdoor activity patterns and the cumulative likelihood of living or vacationing in endemic areas. The median age of diagnosed patients is 53.
How Lyme Disease Compares Globally
Lyme disease is not just an American problem. In Western Europe, an estimated 232,000 cases occur each year. The rates vary enormously by country. Southern Sweden reports the highest incidence in the region at 464 cases per 100,000 people per year. Austria (135 per 100,000) and the Netherlands (134 per 100,000) also have very high rates. By contrast, countries like Italy, Portugal, and Ireland report rates close to zero.
Germany, often considered a Lyme-endemic country, has an incidence of about 37 cases per 100,000 people annually. France sits lower at 9.4 per 100,000. The population-weighted average across Western Europe works out to about 22 cases per 100,000 people per year, though this masks enormous variation even within individual countries. A hiker in southern Sweden faces a vastly different risk profile than someone in southern Spain.
Why Testing Misses Early Cases
Part of the reason Lyme disease is underdiagnosed is that standard blood tests perform poorly in the early stages of infection. The standard two-tier testing approach, which looks for antibodies your immune system produces in response to the bacteria, has a sensitivity of only 17% to 78% in early-stage disease. For patients with a single bull’s-eye rash and early localized infection, that sensitivity drops to just 14.1%. Your body simply hasn’t had time to mount the immune response the test is looking for.
The picture improves dramatically in later stages. For late-stage Lyme disease, the same testing approach catches 96% to 100% of cases. This creates a frustrating clinical reality: the test works best when the disease has already progressed, and performs worst during the window when early treatment would be most effective. This is why many doctors in endemic areas will treat based on symptoms and a plausible tick exposure rather than waiting for lab confirmation.
What the Numbers Mean for Your Risk
If you live in or visit the Northeast, upper Midwest, or mid-Atlantic states, Lyme disease is genuinely common. With nearly half a million Americans diagnosed annually, it’s not a rare or exotic condition in these areas. Your personal risk depends heavily on how much time you spend in wooded or grassy environments during tick season, whether you check for ticks after being outdoors, and how quickly you remove any attached ticks. Transmission typically requires a tick to be attached for 36 to 48 hours, so daily tick checks are one of the most effective preventive measures.
Outside the endemic regions, Lyme remains relatively uncommon, though not impossible. The expanding geographic range means that residents of states previously considered low-risk should stay aware, particularly if they notice an expanding circular rash or develop flu-like symptoms after spending time outdoors in tick habitat.