By Kelly A. Reynolds, MSPH, PhD

At press time, states were just beginning to lift restrictions around America, allowing previously deemed non-essential businesses to reopen. Many businesses are opening in a phased approach, serving clients at dramatically reduced capacity. Regardless of how businesses are choosing to reopen, a universal concern is that each considers the necessary precautions to minimize exposures to infectious microbes. While the world is intently focused on coronavirus, other harmful microbes, like Legionella, may be growing in the stagnant water of community distribution systems and closed building pipes.

What is Legionella?
Before SARS-CoV-2, the causative agent of COVID-19, a pathogen of primary concern in the US was Legionella pneumophila, the causative agent of Legionnaire’s disease. Legionella is a water-based pathogen, meaning it is naturally present in water. It is commonly spread via aerosols created from showers, faucets, fountains or a variety of other equipment. Breathing in contaminated aerosols provides an entry point to the lungs. At low levels, Legionella rarely causes infection but higher concentrations and longer exposure durations increase one’s risk. People over the age of 50 and especially those who smoke or suffer from chronic illnesses, such as lung disease or who are immunocompromised, are at the highest risk of infection and more severe health outcomes.

Legionnaire’s disease is a pneumonia characterized by symptoms of cough, shortness of breath, muscle aches, headache and fever. The organism can also cause a mild, flu-like illness, known as Pontiac Fever. Ten percent of people who contract Legionnaire’s disease will die from the illness. During the most recent (2013-2104) survey of waterborne disease outbreaks, Legionella was responsible for 57 percent of the 42 outbreaks and 100 percent (n=13) of the deaths associated with potable water.1 Cases are documented most frequently in large water systems typical of hotels, hospitals and long-term care facilities, and have dramatically increased in the last two decades.

Stagnant water risks
The national nonprofit, Alliance to Prevent Legionnaire’s Disease (ALPD), has taken to the newswire to warn and educate the public on the increased risk of Legionnaire’s disease, especially given increased risks associated with the pandemic-driven shutdown of businesses, schools, dormitories and personal residences (i.e., vacation homes).2 The organization has developed a new open letter and resource guide aimed at government officials, public health and water safety agencies, building owners and consumers. The guide contains best practices for reducing Legionella risks as buildings reopen after weeks of closure.3

The open letter highlights permissive conditions for bacterial growth in premise plumbing and distribution systems, including the water age, stagnation, dissipation of disinfectants, temperature (optimal growth range= 77-108°F) and other factors. Buildings that have been closed for weeks to months present a high risk of exposure to opportunistic bacterial pathogens that persist in plumbing biofilms. In addition to Legionella, other harmful bacteria can grow in stagnant plumbing water, including Pseudomonas aeruginosa and non-tuberculosis Mycobacterium species, both associated with serious respiratory and lung infections. The proliferation of these organisms rapidly occurs once permissive conditions are established.

Large buildings such as healthcare facilities and hotels are especially concerning due to the large number of water outlets to target for management and control, along with the likelihood of serving vulnerable populations. Information is available to help business owners reopen, while ensuring a safe water supply. The APLD created the resource guide to educate and empower the public to reduce their risk of bacterial exposures from stagnant piped water. The guide is divided into three sections: 1) Water Utilities: Actions to Take; 2) Facility Owners/Managers: Recommissioning Shuttered Buildings and 3) Legionnaires’ Disease: Understanding the Basics.

In the first section, short- and long-term actions are recommended for utility managers. Developing and distributing communication materials to building owners and encouraging the flushing of water mains are important firsts steps. Expanded water testing to closely monitor water quality and verify disinfectant residuals are essential next steps. Careful maintenance and monitoring of disinfectants and pressure should continue to be long-term priorities.

Utilities are not directly responsible for the quality of water delivered to premises. After the water meter, facility owners and managers are expected to be knowledgeable in the management and safe delivery of the water supply to building users (part 2 of the APLD guidance document). Water heaters, cooling towers, humidifiers, faucets, toilets, showers hoses, fountains, whirlpools and spas, POU/POE water filters, aerators, ice machines and more are potential point sources for exposure. Finally, part 3 of the APLD guidance is focused on weekly maintenance tasks to keep water systems operating properly.

Guidance on Legionella prevention
Detailed guidance and training on how to develop a water management plan are provided by The American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) and the Centers for Disease Control and Prevention (CDC). These guidelines have been updated and made increasingly visible in recent years due to an increase in recognition of the widespread and common problem of Legionnaire’s disease. ASHRAE’s guideline has become an industry standard (Standard 188- 2018 Legionellosis: Risk Management for Building Water Systems) that clearly outlines minimum risk management steps for building water systems.4 The CDC’s document is in the format of a toolkit with a one-page questionnaire aimed at assessing the need for actions outlined in a free training.5 The PreventLD Training was developed by researchers at the University of Arizona’s Zuckerman College of Public Health, the CDC, the National Network of Public Health Institutes (NNPHI) and others.6

Additional guidance on how to reopen buildings following the unprecedented shutdown from the pandemic coronavirus outbreak is updated frequently on the CDC website and includes information on mold abatement as well as Legionella controls.7 Both organisms can grow to unacceptable and harmful levels in just weeks, depending on building characteristics. Changes in water conditions can also promote biofilm growth, pipe corrosion and lead leachates.

The first steps in managing building water quality are to ensure that water heater temperatures are set to at least 140°F and to flush hot and cold water through all points of use when reopening a building that has been shuttered for weeks or more. Any equipment used to process or distribute water (i.e., fountains, tubs, spas, etc.) should be flushed, cleaned and sanitized. Readers are strongly encouraged to review the full CDC and ASHRAE guidance for a complete overview of infection control interventions required.

Approximately 90 percent of Legionella outbreaks are thought to be preventable. Preventing Legionnaire’s disease, however, requires strict management of the building water supply and intentional application of controls when water use disruptions occur, such as with the COVID-19 business shutdown. A final note of caution: the premise plumbing flushing and equipment cleaning process may expose individuals to high levels of hazards. Thus, great care should be taken to protect workers and other vulnerable populations. Responsible individuals should wear properly fit and certified N95 respirators as per the Occupational Safety and Health Administration (OSHA) standard8 and high-risk populations should delegate the task altogether.


  1. Benedict KM, Reses H, Vigar M, et al. Surveillance for Waterborne Disease Outbreaks Associated with Drinking Water—United States, 2013–2014. MMWR Morb Mortal Wkly Rep. 2017;66(44):1216-1221. doi:10.15585/mmwr.mm6644a3
  2. APLD: Advocacy Group Warns COVID-19 Shut Down Increases Risk Of Legionnaires’ Disease. Accessed May 17, 2020.
  3.  APLD Resource Guide—PreventLegionnaires. Accessed May 17, 2020.
  4. ASHRAE. ANSI/ASHRAE Standard 188-2018, Legionellosis: Risk Management for Building Water Systems. Published 2018. Accessed April 19, 2019.
  5. CDC. Developing a Water Management Program to Reduce Legionella Growth & Spread in Buildings A PRACTICAL GUIDE TO IMPLEMENTING INDUSTRY STANDARDS. 2017. Accessed April 19, 2019.
  6. CDC, UAMEZCOPH, WWPHTC N. Preventing Legionnaires’ Disease (PreventLD Training). Published 2018. Accessed April 19, 2019.
  7. Guidance for Reopening Buildings After Prolonged Shutdown or Reduced Operation. CDC. Accessed May 17, 2020.
  8. 1910.134–Respiratory Protection. Occupational Safety and Health Administration. Accessed May 17, 2020.

About the author
Dr. Kelly A. Reynolds is a University of Arizona Professor at the College of Public Health; Chair of Community, Environment and Policy; Program Director of Environmental Health Sciences and Director of Environment, Exposure Science and Risk Assessment Center (ESRAC). She holds a Master of Science Degree in public health (MSPH) from the University of South Florida and a doctorate in microbiology from the University of Arizona. Reynolds is WC&P’s Public Health Editor and a former member of the Technical Review Committee. She can be reached via email at


Comments are closed.