Some Businesses May Be At Risk for Legionnaires’ Disease

When businesses are closed for a period of time, water and air conditioning may be shut off to conserve resources. In doing so, the warmth and lack of clean water flow is the right formula for the growth of potentially dangerous microbes, including the bacteria that contributes to Legionnaires’ disease. Any commercial facility vacated or underutilized for more than three weeks, according to health experts and government officials, is at risk for a Legionnaires’ outbreak.

What is Legionnaires’ Disease?

Legionnaires’ disease is a severe, sometimes lethal form of pneumonia caused by Legionella bacteria that builds up in pipes. It got its name from a deadly outbreak following a 1976 American Legion convention in a Philadelphia hotel. The bacteria were ultimately discovered in the cooling tower of the hotel’s air conditioning system.

It leads to death in about one in 10 cases, according to the Centers for Disease Control and Prevention (CDC). The National Academies of Science, Engineering, and Medicine (NASEM) estimates that over 52,000 Americans suffer from the disease each year.

What Causes Legionnaires’ Disease?

Commercial buildings shuttered for weeks or months leads to stagnant water in these dormant buildings. Stagnant or standing water in plumbing can decrease temperatures to the Legionella growth range (77–108°F). It can also lead to low or undetectable levels of disinfectant, such as chlorine. The lack of chlorinated water flowing through pipes, combined with irregular temperature changes, creates conditions ripe for the Legionella bacteria that causes Legionnaires’ disease. As a result, the hot and cold tap water systems—including storage tanks, showers, ice machines, drinking fountains and water softeners—can become unsafe.

Other potential sources of Legionella include:

  • sprinkler systems
  • air conditioning
  • toilets
  • decorative fountains
  • hot tubs
  • eyewash stations
  • safety showers
  • humidifiers
  • idle cooling towers

Your Risk of Exposure

If water containing Legionella is released from any of these systems in a manner that produces aerosol, mist or droplets, these can be inhaled and cause a serious, sometimes fatal pneumonia.

Those most at risk include, but are not limited to:

  • schools
  • gyms
  • factories
  • hotels
  • restaurants
  • outpatient surgical centers

When diagnosed early, Legionnaires’ disease poses a minimal health risk. Most cases can be successfully cured with antibiotics and Legionnaires’ cannot be spread from human to human contact.

Controls to Prevent a Legionnaires’ Outbreak

At a minimum, water systems will likely need to be flushed, cleaned, disinfected and recommissioned. After being remediated, they should be tested to verify the safety of the water and the presence of adequate disinfectant.

The CDC recommends taking these eight steps to minimize Legionella risk before your business or building reopens.

  1. Develop a comprehensive water management program (WMP) for your water system and all devices that use water. Guidance to help with this process is available from the CDC and others.
  2. Ensure your water heater is properly maintained and the temperature is correctly set.
  3. Flush your water system.
  4. Clean all decorative water features, such as fountains.
  5. Ensure hot tubs/spas are safe for use.
  6. Ensure cooling towers are clean and well-maintained.
  7. Ensure safety equipment including fire sprinkler systems, eyewash stations, and safety showers are clean and well-maintained.
  8. Maintain your water system.

The Washington State Department of Health offers these steps for maintaining systems under low use conditions (but not closed):

  1. Flush cold water systems to maintain temperature and chlorine residual.
  2. Monitor and maintain temperatures in hot water systems at the farthest (distal) fixtures. Or turn off the heating system, drain and flush the hot-water tank and refill with cold water. Then flush the hot water system with the cold-water supply to maintain temperature and chlorine residual similar to the cold-water system.
  3. Measure and record temperature and chlorine residual of the supply water from the utility every day. Use these values, not time, as your optimum target for flushing at your distal measurement sites. Individual buildings have too much plumbing variability for time to be a useful flushing parameter.
  4. Maintain cold-water distribution-free chlorine residuals at or above 0.2 mg/L (mg/L is the same as parts per million (ppm) at low concentrations). Measure it with an approved device. The supplying utility’s chlorine levels may limit your ability to maintain this minimum plumbing distribution residual. Contact your utility to better understand their operating parameters.
  5. Document all measurements and maintenance actions in a daily log.

What is important to remember is that systems must be actively managed and maintained to protect the health of building users.

Providing a Safe Work Environment for Employees

You not only need to think about your customer’s safety, but also the safety of you and your employees. To minimize the risk from both chemical and biological exposure while disinfecting and flushing the building plumbing, appropriate training and personal protective equipment (PPE) should be worn.

You can find guidance on worker safety for Legionella control and prevention on the Occupational Safety & Health Administration (OSHA) website. OSHA provides information about the disease, how to identify likely environmental sources of Legionella, and methods to reduce exposure.

Employees Most at Risk

Employees at elevated risk of developing Legionnaires’ disease are those with weakened immune systems and should consult with a medical provider regarding participation in flushing, cooling tower cleaning, or other activities that may generate aerosols. Employers should advise their employees to report signs or symptoms that might be pneumonia to their supervisor or a designated individual at the workplace. If they have symptoms and work around aerosolized water, special tests are needed to determine whether they have Legionnaires’ disease.

Every building is different and will require different actions based on its plumbing systems, use patterns, and source of water supply. By assessing your hazards and implementing procedures now, you can protect your customers and employees, and minimize the steps needed to safely reopen closed or partially closed facilities.

Additional Resources on Legionnaires’ disease:

Visit Society’s Risk Control Library for additional resources or contact your local Society agent to discuss additional coverage needs for your business.


Pat has broad experience working with contractors, supermarkets, convenience stores, restaurants and the hospitality industry. He is a Certified Safety Professional (CSP), holds the Associate of Risk Management (ARM) designation, Associate of Underwriting (AU) designation, and is a member of the American Society of Safety Engineers (ASSE).

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