How many people actually get Lyme each year?

When a clinician or laboratory identifies Lyme disease, many states report it to CDC’s national surveillance system. A “case” in these charts is one of those reports — not a person who felt ill, not a positive test on its own, but a report that met the surveillance definition in force that year, confirmed plus probable. That definition has changed several times — CDC lists versions dated 1995, 1996, 2008, 2011, 2017 and 2022. The chart above marks the two that added a new way to count a case: 2008, when a probable category was added, and 2022, when high-incidence jurisdictions began counting on laboratory evidence alone. A trend line that hides its own rule changes shows artifacts as epidemiology, and a jump near one of the unmarked versions may also be partly the rules changing.

In 2008 the national case definition added the “probable” category. The chart’s second band begins there, so the step at 2008 is partly a new category being counted, not only new illness.

From 2022, states where Lyme is common report cases on laboratory evidence alone — no clinical write-up required — and nearly all of those land in the “probable” category. That is why the confirmed band collapses and the probable band leaps at the 2022 line: the counting changed more than the illness did. It is also why the 89,469 cases reported for 2023 cannot be laid directly against a 2019 figure — the two years counted differently.

Reported Lyme is intensely regional: the Northeast and the upper Midwest carry most of it. Two things sit inside that pattern and a case count cannot pull them apart — the blacklegged tick is densest there, and since 2022 those are the jurisdictions counting on laboratory evidence alone, so the same illness generates more reports there than it does elsewhere. The tick’s range is far wider than the high-count states: the eastern United States from Maine to Florida, the upper Midwest, and still moving west — the tick identification guide carries the range for each species.

For 2023, 44 jurisdictions have a published count, and 54 further cases sit in the national total without a state — real cases, either withheld from their jurisdiction because the count there was small enough to point at individual people, or published with no jurisdiction attached at all. Read the absences carefully too — a state with no published count either did not report Lyme surveillance data that year or reported a count small enough that CDC withheld it, and neither is the same as having no Lyme. The Lyme map draws every state and every year of this data, with the non-reporting states marked as exactly that.

The curve below counts weeks of report, not weeks of bite. A case joins it only after a rash is noticed, an appointment happens, a test comes back and a report is filed, so the season it draws sits somewhat later than the season that caused it. Reports climb through late spring, peak in mid-July and fall through autumn. The drawing is a single past year, named on the figure itself, and it is kept for the shape — which repeats — rather than for counts that are current. What to actually do about the season belongs to the prevention guide, which covers what works.

Surveillance counts reports, and most diagnosed Lyme is never reported. CDC-published analyses of insurance claims estimate that roughly 476,000 people may be diagnosed with and treated for Lyme disease each year in the United States (Kugeler et al., Emerging Infectious Diseases, 2021; CDC, Lyme disease data and surveillance (opens in a new tab), read 25 September 2026) — several times the surveillance totals above. CDC notes this may be an overestimate, because billing codes do not always reflect a confirmed diagnosis. Both numbers are real; they measure different things. Neither is an infection count, and neither says anything about any one person’s odds.

One more thing worth noticing in these charts: CDC withholds counts that are small enough to point at individual people — that is why the state chart reconciles to the national total only after adding back the cases that carry no state. This platform holds its own counts to a floor of the same kind: no aggregate here is released for a group smaller than five.

Data retrieved from data.cdc.gov on 2026-08-27