Legionnaires' disease

Water management problems can lead to outbreaks

In the last year, about 5,000 people in the United States were diagnosed with Legionnaires’ disease, which is a deadly bacterial lung infection for 1 in 10 people who get it according to a new CDC Vital Signs report.

Unlike most respiratory infections, Legionnaires’ disease is generally not spread from person to person — it is caused by breathing in small water droplets contaminated with Legionella. Looking back over all of the building-associated outbreaks that CDC investigated from 2000 through 2014 showed that almost all of these outbreaks were caused by problems that could have been prevented with more effective water management.

Other key findings in the Vital Signs report show that:

  • The number of people being diagnosed with Legionnaires’ disease in the United States grew by nearly 4 times from 2000 through 2014.
  • Approximately 80% of Legionnaires’ disease outbreaks that CDC investigated from 2000 through 2014 occurred in hotels, long-term care facilities, and hospitals.
  • Most Legionnaires’ disease outbreaks CDC investigated occurred because water systems in buildings were not well maintained; problems identified included process failures, human error, equipment breakdowns, or changes in water quality from reasons external to the building itself that led to growth of Legionella in the water.

CDC is urging building owners and managers to follow newly published standards that promote water management programs aimed at reducing the risk of Legionnaires’ disease. To support building owners and managers in this, CDC released a toolkit on Developing a Water Management Program to Reduce Legionella Growth & Spread in Buildings: A Practical Guide to Implementing Industry Standards. The toolkit interprets the guidance in ASHRAE Standard 188, provides a checklist and many examples to help identify where Legionella could grow and spread, and offers planning solutions to help reduce that risk.

Steps to develop a Legionella water management program include:

  1. Establish a water management program team.
  2. Describe the building water systems using text and flow diagrams.
  3. Identify areas where Legionella could grow and spread.
  4. Decide where control measures should be applied and how to monitor them.
  5. Establish ways to intervene when control limits are not met.
  6. Make sure the program is running as designed and is effective.
  7. Document and communicate all the activities.
Water management problems can lead to Legionnaires' disease outbreaks

Over the last 15 years, the number of people getting Legionnaires’ disease grew by nearly 4 times.

People can get Legionnaires’ disease, a type of serious lung infection (pneumonia), by breathing in small droplets of water that contain Legionella.image icon

People can get Legionnaires’ disease, a type of serious lung infection (pneumonia), by breathing in small droplets of water that contain Legionella.

The number of people with Legionnaires' disease grew by nearly 4 times from 2000-2014.image icon

The number of people with Legionnaires' disease grew by nearly 4 times from 2000-2014.

Legionnaires' disease is deadly for about 10% of the people who get it.image icon

Legionnaires' disease is deadly for about 10% of the people who get it.

CDC investigations show almost all outbreaks were caused by problems preventable with more effective water management.image icon

CDC investigations show almost all outbreaks were caused by problems preventable with more effective water management.

A CDC microbiologist pours water samples from a building experiencing a Legionnaires’ disease outbreak into a filtration system to test for Legionella.image icon

A CDC microbiologist pours water samples from a building experiencing a Legionnaires’ disease outbreak into a filtration system to test for Legionella.

Illustration of Legionella pneumophila, the bacterium that causes the majority of Legionnaires’ disease cases and outbreaks.image icon

Illustration of Legionella pneumophila, the bacterium that causes the majority of Legionnaires’ disease cases and outbreaks.

A CDC microbiologist examines a plate for Legionella growth.image icon

A CDC microbiologist examines a plate for Legionella growth.

Water samples from a building experiencing a Legionnaires’ disease outbreak are unpacked at CDC’s Legionella Laboratory.image icon

Water samples from a building experiencing a Legionnaires’ disease outbreak are unpacked at CDC’s Legionella Laboratory.

CDC scientists in the Legionella laboratory prepare equipment to perform whole genome sequencing of L. pneumophila isolated from environmental samples.image icon

CDC scientists in the Legionella laboratory prepare equipment to perform whole genome sequencing of Legionella pneumophila isolated from environmental samples.

Legionella pneumophila, a bacterium that can cause Legionnaires’ disease, growing on specialized microbiological media (BCYE).image icon

Legionella pneumophila, a bacterium that can cause Legionnaires’ disease, growing on specialized microbiological media (BCYE).

Collecting environmental samples can help disease detectives determine the source of a Legionnaires’ disease outbreak.image icon

Collecting environmental samples can help disease detectives determine the source of a Legionnaires’ disease outbreak.

Environmental health expertise is a key part of investigating Legionnaires’ disease outbreaks. Finding out where Legionella is hiding and removing it from the water systems are the most critical steps to prevent additional cases.image icon

Environmental health expertise is a key part of investigating Legionnaires’ disease outbreaks. Finding out where Legionella is hiding and removing it from the water systems are the most critical steps to prevent additional cases.

infographic of building areas where Legionella can grow.

Legionella can grow and spread in many areas of a building. Common sources of Legionella exposure include water used for showering, cooling towers (parts of large, centralized air conditioning systems), hot tubs, and decorative fountains and water features.

Legionella lives in natural sources of water, but can become a health problem in human-made water systems. To lower the risk of Legionnaires’ disease, it is important to reduce Legionella growth (called amplification) and spread to people when they inhale water droplets (called aerosols).

Legionella lives in natural sources of water, but can become a health problem in human-made water systems. To lower the risk of Legionnaires’ disease, it is important to reduce Legionella growth (called amplification) and spread to people when they inhale water droplets (called aerosols).

Cooling towers, which are often part of the air conditioning systems of large buildings, are a common source of Legionella exposure in outbreaks. Cooling towers need to be properly maintained in order to prevent Legionnaires’ disease.image icon

Cooling towers, which are often part of the air conditioning systems of large buildings, are a common source of Legionella exposure in outbreaks. Cooling towers need to be properly maintained in order to prevent Legionnaires’ disease.

Testing water samples from buildings for Legionella is an important part of investigating Legionnaires’ disease outbreaks.image icon

Testing water samples from buildings for Legionella is an important part of investigating Legionnaires’ disease outbreaks.

Legionella can grow in many parts of water systems in buildings, including water heaters.image icon

Legionella can grow in many parts of water systems in buildings, including water heaters.

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Page last reviewed: June 5, 2020