Legionellosis Surveillance and Trends

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.
Legionnaires' disease is on the rise.

Data systems

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

Keep Reading: Surveillance Systems

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 starting in 2021.

Figure showing reported Legionnaires’ disease incidence has generally been increasing since 2000, with a peak in 2018.
Legionnaires' disease incidence has been increasing since 2000.

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 annual 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.

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