1. Legionella bacterium, the causal agent of Legionnaires’ disease, is a clinically significant environmental pathogen.

Recent developments have resulted in a new, higher standard of care for building owners and managers. ANSI/ASHRAE Standard 188-2015, Legionellosis: Risk Management for Building Water Systems, was published on June 26th, 2015. It was the first industry consensus standard addressing Legionnaires’ disease.

2. Legionnaires’ disease results from inhalation or aspiration of Legionella-contaminated water droplets associated with building water systems such as domestic plumbing and cooling towers. It is NOT transmitted person-to-person.

When Legionella-contaminated aerosols are released into the environment, the droplets can be inhaled and cause pneumonia. About 60% of Legionnaires’ disease cases are in high-risk populations such as smokers, diabetics, and the elderly. The other 40% of cases affect persons that are not in any identified high-risk group.

3. Legionella bacterium are often present in small, sometimes undetectable numbers in EPA-compliant drinking water received by buildings. But building water systems can act like incubators, and a small number of Legionella can grow quickly to very large numbers.

4. Legionnaires’ disease accounts for more than 65% of all reported waterborne disease outbreaks in the US. 

The greatest number of outbreaks of Legionnaires’ disease investigated by CDC between 2000 and 2014 were associated with plumbing (52%), followed by cooling tower water systems (24%). Because relatively more cases are associated with cooling tower outbreaks, the total number of cases from premise plumbing and cooling towers were roughly equivalent. 

5. The number of reported Legionnaires’ disease outbreaks in the US has increased >280% since 2000.

6. Legionnaires’ disease is preventable.

CDC investigations show that almost all the outbreaks investigated were caused by problems preventable with more effective water management. CDC recommends that facilities implement a Legionella water management program for plumbing and cooling tower systems following ANSI/ASHRAE 188-2015:
• Establishing a water management program team.
• Describing the building water systems using words and diagrams.
• Identifying areas where Legionella could grow and spread.
• Deciding where control measures should be applied and how to monitor them.
• Establishing ways to intervene when control limits are not met.
• Making sure the program is running as designed and is effective.
• Documenting and communicating all the activities.


Aaron Rosenblatt

Principal, Gordon & Rosenblatt