EPA Releases Final Guidance on Efficacy Testing of Antimicrobial Pesticides Against Legionella Pneumophila in Cooling Tower Water

Released on August 28, 2024

Today, the U.S. Environmental Protection Agency (EPA) released the final guidance and a test method to evaluate efficacy claims for antimicrobial products against Legionella pneumophila (L. pneumophila) in cooling tower water. Legionnaires’ disease (LD) is a serious type of pneumonia (lung infection) acquired by breathing in water droplets contaminated with L. pneumophila bacteria. Cooling towers are a potential breeding ground for this bacterium. L. pneumophila can disperse through the air in water droplets if cooling towers are not properly maintained. The incidence of LD in the United States has been increasing since 2000. Outbreaks and illness clusters have been associated with decorative, recreational, domestic, and industrial water systems, with the largest outbreaks caused by cooling towers. Since 2006, for example, six community-associated LD outbreaks have occurred in New York City, resulting in 213 cases and 18 deaths. More recently, in August 2024, the New Hampshire Department of Health and Human Services identified seven individuals diagnosed with LD, linked to the presence of L. pneumophila in a nearby cooling tower.

Under the Federal Fungicide, Insecticide, and Rodenticide Act (FIFRA), antimicrobial pesticides that claim to kill harmful microbes must be registered with EPA before they can be sold or distributed in the United States. Companies seeking to add efficacy claims for antimicrobial products against L. pneumophila must submit appropriate efficacy data to the Agency for review and approval to support these claims. EPA has worked collaboratively with industry to develop a test method that simulates the normal operating conditions of cooling tower water to assess the efficacy of antimicrobial pesticides designed to kill free-floating L. pneumophila bacteria. In October 2023, EPA released the draft guidance and test method for public comment. The Agency received comments regarding clarifications and proposed revisions to the draft guidance and method, as well as suggestions for future expansion of the guidance. After considering the public comments, EPA made several revisions to the draft guidance to clarify and simplify the content and address concerns pertaining to efficacy testing using oxidizing chemistries. EPA is releasing the final guidance and test method documents, as well as a response to comments document.

The finalized guidance provides an overview of the test method and additional information to registrants seeking to add L. pneumophila claims. The additional information includes data submission procedures, and example pesticide label use directions and claims for proposed antimicrobial product labels. Antimicrobial products with L. pneumophila claims may be used as part of a water management plan for cooling tower systems. These water management plans would include routine maintenance and remediation treatments as recommended by the American Society of Heating, Refrigerating and Air-Conditioning Engineers standards and applicable federal, state, or local regulation(s). Operating cooling towers in accordance with water management plans will ensure that the towers are maintaining conditions that are appropriate for treatment with an antimicrobial product.

The final guidance, test method and the agency’s response to public comments are available in docket EPA-HQ-OPP-2023-0430 at www.regulations.gov.