Education · Surveillance data

Lyme, counted

CDC has counted reported Lyme disease cases since the early 1990s. The counts are real, public, and worth reading — and they only make sense with their caveats attached. This page shows the numbers the way they deserve to be shown: with the counting rules drawn in.

What a reported case is

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. That definition has changed twice, and both changes are drawn into the chart below, because a trend line that hides its own rule changes shows artifacts as epidemiology.

Thirty-two years, counted three ways.

Reported Lyme disease cases in the United States, 1992 through 2023Reported cases rose from 9,908 in 1992 to 89,469 in 2023, but the line is not one measurement: the surveillance case definition changed twice. From 2008 a Probable category was added beside Confirmed — 2019, for example, is 23,453 confirmed plus 11,492 probable. From 2022 high-incidence states count laboratory evidence alone, and most cases land as Probable: of the 89,469 cases in 2023, 85,938 are probable and 3,531 confirmed. The jumps at those two boundaries are partly changes in counting, not only changes in illness.030K60K90K2008 · PROBABLE ADDED2022 · REVISEDCONFIRMEDPROBABLE89,4699,90819922000200820162023
  • Confirmed cases
  • Probable cases (category exists from 2008)

The 2023 total is nine times 1992’s — and the steepest jumps sit exactly on the two definition changes, which is a fact about surveillance as much as about ticks.

Reported cases are what surveillance captured, not what happened: CDC's own claims-based analyses estimate several times more people are diagnosed and treated each year than surveillance reports. Comparing years across a marked boundary compares definitions as well as illness.

CDC national Lyme disease surveillance via data.cdc.gov (datasets 84rx-ksgd 1992-2007, qtbi-xd4i 2008-2021, x5j9-wybp 2022-2023). Every number here is taken from CDC and checked against their own published totals, then re-checked against the live source so a figure CDC revises cannot quietly stay wrong here.

What changed in 2022

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.

Comparing years across a definition change compares the definitions too. The direction across three decades — sustained growth — survives every definition; the size of any single jump at a marked boundary does not.

Where the reports come from

Reported Lyme is intensely regional: the Northeast and the upper Midwest carry most of it, which is the blacklegged tick’s home range. Read the absences carefully — 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.

Reported Lyme lives in a handful of states.

Reported Lyme disease cases by state, 2023, top twelve jurisdictionsNew York reported the most Lyme disease cases to CDC for 2023 at 22,173, then Pennsylvania at 16,671 and Massachusetts at 9,715, with New Jersey, Wisconsin, West Virginia, Connecticut, Maine, Minnesota, Rhode Island, Maryland and Virginia completing the top twelve. Only 44 jurisdictions have a published count — a state absent from the data either did not report or had its count withheld by CDC as too small to show, and neither is the same as having no cases — and 54 further cases are suppressed below state level by CDC.NY22,173PA16,671MA9,715NJ7,224WI6,283WV3,242CT3,239ME2,942MN2,938RI2,852MD2,470VA1,747

The Northeast and upper Midwest dominate the 2023 reports — the same geography the blacklegged tick calls home.

Top twelve of the 44 jurisdictions with a published count. A state absent from the data either did not report Lyme surveillance data to CDC for 2023 or reported a count CDC withheld as too small to show — absence here is not evidence of absence there — and 54 further cases are suppressed below state level. Counts mix Confirmed and Probable under the revised 2022 definition.

CDC Lyme disease surveillance, 2023, via data.cdc.gov (dataset x5j9-wybp; confirmed plus probable). Every state figure here comes straight from CDC and adds up to their own published national total. We re-check it against the live source, so a number CDC revises cannot quietly stay wrong here.

The year has a shape

Weekly reports climb through late spring, peak in mid-July, and fall through autumn — the same window when nymph-stage ticks are active and people are outdoors. If prevention effort has a season, it is the rise of that curve, not its peak: the prevention guide covers what actually works.

The year has a shape.

Reported Lyme disease cases by week of the year, United States, 2014Weekly national Lyme disease reports through 2014 climb from around ten cases a week in January to a peak of 509 in week 28 — mid-July — then fall through autumn. The summer wall lines up with nymph season: the smallest, hardest-to-spot tick stage is most active exactly when people are outdoors most. The shape repeats year over year; the counts shown are 2014’s.0250500WEEK 28 · 509JFMAMJJASOND

Prevention effort is worth most exactly where the wall rises — late spring, before the July peak, when nymphs are out and people are too.

One historical year (2014), kept for its shape — the seasonal pattern repeats, the absolute counts are that year's. Weekly figures are provisional reports; the shallow first and last weeks owe as much to reporting lag as to ticks.

CDC national notifiable disease surveillance, weekly table II, via data.cdc.gov (dataset y6uv-t34t, United States rows, weeks 1-53 of 2014 — a historical series kept for its seasonal shape). Taken straight from CDC and re-checked against the live source, so a revised figure cannot quietly stay wrong here.

What counting cannot see

Surveillance counts reports, and most diagnosed Lyme is never reported. CDC-published analyses of insurance claims estimate that roughly 476,000 people are diagnosed with and treated for Lyme disease each year in the United States (Kugeler et al., Emerging Infectious Diseases, 2021) — several times the surveillance totals above. Both numbers are real; they measure different things.

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 suppressed cases. The research commons on this platform applies the same discipline: no aggregate is ever released for a group smaller than five.

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

Nothing on this page is a diagnosis or a risk score, and a rising count is not a statement about you. These are public surveillance figures, shown with the rules that produced them, so that the numbers you meet elsewhere have context.

Related guides: The Lyme map · Understanding ticks · Testing guide · Education library