The Legionnaires’ disease rate climbed 19% in 2025 to nearly its 2018 peak, according to provisional CDC data.
The CDC monitors legionellosis cases through two surveillance systems — the National Notifiable Diseases Surveillance System and the Supplemental Legionnaires’ Disease Surveillance System. It reports rates as cases per 100,000 population.
Cases of Legionnaires’ disease have steadily increased since the early 2000s, and peaked in 2018. Reported cases dropped steeply in 2020, then rebounded in 2021.
Here is what to know.
1. In 2018, there were 3.04 cases per 100,000 population. Provisional 2025 data show there were 2.9 cases per 100,000, up from 2.44 in 2024.
2. In 2025, New York City and West Virginia had the highest Legionnaires’ disease rates among states at 7.8 and 7.18 per 100,000, respectively. Meanwhile, Alaska and Delaware had the lowest rates at 0.41 and 0.57, respectively.
3. Rates were highest among Black people, men and older adults.
4. The Northeast and Midwest regions had the highest reported cases among CDC regions.
5. Summer and fall months had the highest rate of reported cases.
