EPA Releases Draft Guidance on Testing the Efficacy of Antimicrobial Pesticides Against Legionella Pneumophila in Cooling Towers

Released on October 2, 2023

Today, EPA released for public comment a draft guidance with a test method to evaluate efficacy claims for antimicrobial products against Legionella pneumophila (L. pneumophila) in cooling tower water.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. Aerosolization of L. pneumophila can occur 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 being caused by cooling towers. Since 2006, six community-associated LD outbreaks have occurred in New York City, resulting in 213 cases and 18 deaths.

Under federal law, antimicrobial pesticides that claim to kill harmful microbes must be registered with EPA before they can be sold or distributed in the United States. The Agency must receive and review appropriate efficacy data 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 pesticides designed to kill free-floating L. pneumophila bacteria. In cooling towers, L. pneumophila may exist in multiple forms, including in biofilm attached to the surfaces or inside larger host organisms such as amoeba. This proposed guidance and test method is not intended to address these other forms.

When finalized, the guidance would support antimicrobial products claiming to reduce free-floating L. pneumophilia to be used in water management plans for cooling tower systems, providing a multi-barrier approach to reduce the bacterium in cooling tower water. 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/or applicable federal, state, or local regulation(s). Operating cooling towers in accordance with water management plans will ensure that the cooling towers are maintaining conditions that are appropriate for treatment with an antimicrobial product.

The draft guidance is available for public comment in docket EPA-HQ-OPP-2023-0430 at www.regulations.gov for 60 days.