CDC Releases New Document for Controlling Legionella Bacteria

By Hilary Nardone, Environmental Group Training Manager
Certified ASSE 12080 Legionella Water Safety and Management Specialist

The Centers for Disease Control and Prevention (CDC) recently released a “Toolkit for Controlling Legionella in Common Sources of Exposure” (Legionella Control Toolkit). The aim of this new document is to provide building owners and operators with “concise, actionable information on controlling Legionella in commonly implicated sources of Legionnaires’ disease outbreaks.” This document can be used to:

As part of the Legionella Control Toolkit, the CDC has included guidance on routine testing for Legionella bacteria. Prior to this publication, the CDC had not previously published guidance for routine environmental Legionella bacteria sampling. This new tool helps to “analyze hazards and establish Legionella control measures per ASHRAE Guideline 12-2020.”Routine sampling should be part of a facility’s Legionella bacteria control and prevention plan and should be representative of the entire water system.

While there is no known “safe” level or type of Legionella bacteria, the CDC has created a diagram to help in interpreting positive environmental Legionella bacteria results:

The CDC has determined that in potable water systems, positive Legionella bacteria samples greater than 1.0 CFU/mL indicates a poorly controlled system. This is in line with ASHRAE Guideline 12-2020, which recommends remediation action on any positive Legionella bacteria sample that is greater than 1.0 CFU/mL. Results may indicate the need for a short- or long-term remediation, including the installation of supplemental disinfection such as Barclay’s iChlor® monochloramine system. After each remediation, it is important to resample for Legionella bacteria to validate its effectiveness.

Not only is routine Legionella bacteria sampling helpful in interpreting a well-controlled water system, it also validates the effectiveness of a facility’s Water Management Program (WMP), which is a requirement per ASHRAE Standard 188. Samples that are non-detect for Legionella bacteria indicate that the WMP’s critical control locations are being monitored correctly.

Barclay Water Management, Inc. is an industry leader in Legionella bacteria risk minimization by offering sampling and testing programs to detect Legionella bacteria in potable and non-potable water systems. We can help determine the appropriate number and location of samples to ensure our customer’s unique needs are met. We then provide each customer with results along with result interpretations and relevant recommendations. Barclay’s third-party laboratory is accredited by the CDC ELITE Legionella Program and the New York Environmental Laboratory Approval Program.

Barclay has created, implemented, and validated hundreds of WMPs in partnership with our customers. Barclay continually utilizes best practice recommendations from organizations including but not limited to ASHRAE, CIBSE, CDC to minimize waterborne pathogens in building water systems and is dedicated to ensuring its WMPs comply with national and local standards and guidelines including ASHRAE Standard 188, CMS, local Health Departments, and the Joint Commission.


1.CDC.Toolkit for controlling Legionella in common sources of exposure. CDC. Updated February 3, 2021. Accessed February 23, 2021.

2.CDC.Routine testing for Legionella. CDC. Updated February 3, 2021. Accessed February 23, 2021.

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