Report within 24 hours of Diagnosis to the Local Health Department.

Legionnaires' disease and Pontiac fever are collectively known as legionellosis, a disease caused by Legionella bacteria. Legionella is a type of bacterium found naturally in freshwater environments, like lakes and streams. It can become a health concern when it grows and spreads in human-made water systems such as building premise plumbing and cooling towers (structures that contain water and a fan as part of centralized air-cooling systems for building or industrial processes). Legionella can continue to persist in the water system unless proper steps are taken to prevent the growth of bacteria.

People can get Legionnaires’ disease or Pontiac fever when they breathe in small droplets of water in the air that contain the bacteria. People can breathe in small droplets of water by using a shower, hot tub, or sink. Other sources of aerosolized water include decorative fountains and cooling towers.

Less commonly, people can get sick by aspiration of drinking water containing Legionella. This happens when water accidentally goes into the lungs while drinking. People at increased risk of aspiration include those with swallowing difficulties.

Note: Home and car air-conditioning units do not use water to cool the air, so they are not a risk for Legionella growth.

General Public

• Guidance for Removing and Cleaning a Shower Head 
• Frequently Asked Questions
• CDC Fact Sheet [English] [Spanish]
• Legionnaires’ Disease and Your Household Water
• Guidance for Draining and Flushing Your Water Heater 

Building Owners/Managers

• Water Management Program Template 
• Legionella and Supplemental Disinfection Systems 
• Maintaining Building Water Systems Prevents Legionnaires’ Disease
• Maintaining and Reopening Building Water Systems Impacted by Prolonged Shutdown or Reduced Operation: Minimizing Legionella and Opportunistic Bacteria Growth
• CDC Infographic: How Legionella affects building water systems and people
• CDC Toolkit: Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings
• CDC Toolkit: Toolkit for Controlling Legionella in Common Sources of Exposure

Local Health Department Resources

• Standard Operating Procedure: Legionnaires' Disease Outbreak Investigations
• Guidance for Selecting Environmental Consultants
• Guidance for Environmental Legionella Sampling and Testing
• Legionella Environmental Assessment Form (LEAF)
• Legionella Environmental Data Collection Sheet (Excel document)
• Guidance for Responding to Post-Remediation Environmental Legionella Detections
• Notification to a Healthcare Facility Associated with a Presumptive Healthcare-Associated Case (template letter)
• Notification to a Healthcare Facility Associated with Two or More Possible Healthcare-Associated Cases (template letter)
• Notification to a Facility (non-Healthcare) Associated with Two or More Cases within 12 Months (template letter)
• Dear Cooling Tower Operator Letter

Healthcare Providers

• Guidance for Submitting Clinical Specimens for Legionella Testing UPDATED 2/27/25
• CDC Fact Sheet: What Clinicians Need to Know about Legionnaires' Disease
• CDC Vital Signs (2016): Legionnaires’ Disease Outbreaks [English] [Spanish]
• CDC Checklist: Healthcare Facility Water Management Program
• CDC Vital Signs (June 2017): Legionnaires’ Disease
• CDC Reduce Risk from Water
• CMS Memo (June 2017): Requirement to Reduce Legionella Risk in Healthcare Facility Water Systems to Prevent Cases and Outbreaks of Legionnaires’ Disease

• Legionella Investigation for Local Health Departments webinar slides (6/22/21)

• A Deeper Dive into Legionella Outbreak Investigation for Local Health Departments webinar slides (12/01/21) 

• Preventing Legionnaires’ Disease: A Training on Legionella Water Management Programs (PreventLD Training)