Environmental Assessment and Sampling Resources


  • An environmental assessment is the part of an outbreak investigation that determines where conditions could support Legionella growth and spread.
  • Explore our resources to assist with the environmental component of Legionnaires' disease outbreak investigations.
People taking water samples next to a hot tub.

Printable resources

Top portion of the environmental assessment form.
Use our Legionella Environmental Assessment Form (LEAF).
  • Legionella Environmental Assessment Form (UPDATED March 2022) - Use this fillable form to document a facility's water systems, help determine whether to conduct Legionella environmental sampling, and, if so, develop a sampling plan.
  • Legionella Environmental Assessment Form Marking Guide - Use this instructional resource to complete the Legionella Environmental Assessment Form and increase awareness of conditions that may promote Legionella growth and spread.
  • CDC Sampling Procedure and Potential Sampling Sites (UPDATED Jun 2019) - Use this protocol to collect environmental samples for Legionella culture during an outbreak investigation or when cases of disease may be associated with a facility (includes sampling supply checklist).
  • Sample Data Sheet (UPDATED Jun 2019) - Use this form to keep track of environmental samples taken for Legionella culture during an investigation.

Instructional videos

Person swabbing a water faucet.
Watch six instructional videos on environmental aspects of outbreak investigations.
  • Legionella Ecology and an Introduction to Environmental Health and Engineering - Learn why and where Legionella grows as well as the basics of how cooling towers, premise plumbing, and whirlpool spas (hot tubs) work. (Length: 14:49)
  • Conducting and Interpreting the Environmental Assessment - Learn useful tips about conducting an environmental assessment and how to interpret the results of key questions on CDC's Legionella Environmental Assessment Form. (Length: 10:12)
  • How to Make a Sampling Plan - Taking water and biofilm samples for Legionella testing is an important step in an outbreak investigation. Learn how to make a plan for the number of samples to take and where to take them. (Length: 5:14)
  • How to Sample Potable Water - Learn CDC's procedure for collecting potable water samples for Legionella culture during a cluster or outbreak investigation, or when cases of disease may be associated with a facility. (Length: 7:11)
  • How to Sample Cooling Towers - Learn CDC's procedure for collecting environmental samples from a cooling tower for Legionella culture during a cluster or outbreak investigation, or when cases of disease may be associated with a facility. (Length: 5:15)
  • How to Sample Spas and Fountains - Learn CDC's procedure for collecting environmental samples from spas (hot tubs) and fountains for Legionella culture during a cluster or outbreak investigation, or when cases of disease may be associated with a facility. (Length: 7:32)

Cooling tower resources

Photo example of a cooling tower with fan blades
Identify cooling towers with our strategies and photos.

Cooling towers can cause outbreaks of Legionnaires' disease when they are not adequately maintained. In an outbreak scenario, identifying cooling towers quickly and accurately is essential to limiting the number of people exposed. However, searching for cooling towers during an outbreak can be difficult.

Training and toolkits on controlling Legionella

Graphic showing instructor looking at information on a screen.
Learn to create a water management program with our training.

PreventLD Training - Take this training from CDC and partners on creating a water management program to reduce risk for Legionnaires' disease. PreventLD Training aligns with industry standards (ASHRAE 188) on managing risk for Legionella bacteria.

Toolkit: Developing a Legionella Water Management Program - Learn how to develop a water management program to reduce Legionella risk.

Toolkit: Controlling Legionella in Common Sources of Exposure - Find actionable information on Legionella control measures.

More resources and scientific publications


Legionella Reference Center quick reference guide - This reference center accepts testing requests from enrolled governmental public health or environmental laboratories. It performs Legionella testing on clinical specimens and isolates, as well as preapproved outbreak samples.

Key findings: Outbreaks and water management gaps - Analysis of reports from CDC-led investigations of LD outbreaks. All of the deficiencies associated with outbreaks could have been prevented by comprehensive, properly implemented water management programs (WMPs).


Clopper B, Kunz J, Hannapel E. Preventing Legionnaires' disease: Frontline tools for environmental health practitioners. [commentary] J Environ Health. 2021;83(8):32-4.

Hunter CM, McMullen S, Edens C, Baddour LJ, McKeever J, Reynolds KA, et al. Preventing Legionnaires' disease through a new learning opportunity: A training on Legionella water management programs. [commentary] J Environ Health. 2019;82(3):44-6.

James AE, Kesteloot K, Paul J, McMullen RL, Louie S, Waters C, et al. Potential association of Legionnaires' disease with hot spring water, Hot Springs National Park and Hot Springs, Arkansas, USA, 2018–2019. Emerg Infect Dis. 2022;28(1):44-50. (Ritter T, Kunz J)

Mac VV, Labgold K, Moline HL, Smith JC, Carroll J, Clemmons N, et al. Notes from the field: Legionnaires disease in a U.S. traveler after staying in a private vacation rental house in the U.S. Virgin Islands — United States, February 2022. MMWR. 2023;72(20);564-5. (Kunz J)

Rispens JR, Hast M, Edens C, Ritter T, Mercante JW, Siegel M, et al. Legionellosis cluster associated with working at a racetrack facility in West Virginia, 2018. J Environ Health. 2021;83(6):14-9.