Legionellosis Surveillance and Trends

For Public Health

Key points

  • Legionellosis (Legionnaires' disease and Pontiac fever) is a nationally notifiable condition in the United States.
  • CDC conducts national surveillance for legionellosis using two surveillance systems.
  • View the most recent data and trends for Legionnaires’ disease.
Legionnaires' disease is on the rise.

Data systems

CDC monitors legionellosis cases through two surveillance systems at the national level.

Keep Reading Methods for Legionnaires' Disease Surveillance

How the data are interpreted

Disease trends

In general, reported cases of Legionnaires' disease have been increasing since the early 2000s, with a peak in 2018. While reported cases dropped during the first year of the COVID-19 pandemic, they rebounded in 2021.

Explore the data

Use the figure below to see reported U.S. Legionnaires' disease incidence from the National Notifiable Diseases Surveillance System (NNDSS) since 2000. The incidence for years highlighted in the grey vertical bar is based on provisional data. You can also view the data in table format by clicking on "Data Table" beneath the figure.

Use the figure below to see reported U.S. Legionnaires' disease incidence by jurisdiction from NNDSS for 2014 through 2025. The incidence for 2024 and 2025 is based on provisional data. Filter by year by clicking on the drop-down arrow under the word "Year." You can also view the data in table format by clicking on "Data Table" beneath the figure.

Some groups have higher incidence rates

Rates of reported cases of Legionnaires' disease are highest in

  • Black persons
  • Males
  • Older adults
  • Northeast and Midwest regions
  • Summer and fall months

Data reporting

Data from surveillance systems were combined to provide a more comprehensive understanding of the national burden of Legionnaires' disease. The following surveillance reports provide a descriptive summary of the reporting and burden of Legionnaires' disease within the United States.

Report topics include:

  • Case count and incidence
  • Seasonality and geographic distribution
  • Demographic characteristics
  • Potential exposure sources
  • Disease severity indicators
  • Diagnostic laboratory test results

Data definitions

The Council of State and Territorial Epidemiologists released the most recent case definition for legionellosis in 2020.

Keep Reading About the Data: Case Definitions

Strong surveillance helps to quickly identify new cases, epidemiologic links between cases, and the need for outbreak investigations.

Keep Reading About the Data: Case Report Forms and Instructions
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Content Source:
National Center for Immunization and Respiratory Diseases; National Center for Environmental Health