Legionella Testing

What is ASHRAE 188?

ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) Standard 188 establishes the minimum legionellosis risk-management requirements for building water systems. This standard is intended for owners and managers of human-occupied buildings, excluding single-family residential buildings.

About Legionellosis

Legionella bacteria are found naturally in freshwater environments, such as lakes and streams. When the bacteria grow and spread in human-made building water systems, it can become a health concern.

The bacterium L. pneumophila was first identified in 1976 as the cause of a severe pneumonia outbreak at the American Legion Convention in Philadelphia. Researchers have since linked Legionellosis outbreaks to aerosol mist generation within poorly-maintained artificial water systems containing elevated levels of the Legionella bacteria.

“Legionellosis” refers to two distinct clinical illnesses:

  1. When the bacterium Legionella causes pneumonia, the disease is referred to as “‘Legionnaires’ Disease” (LD). The Centers for Disease Control and Prevention (CDC) estimates that there are between 8,000 and 18,000 cases of LD each year in the United States. More than 10% of LD cases are fatal.
  2. Legionella can also cause a less-severe influenza-like illness known as “Pontiac fever.”

Common Sources of Infection

Legionella bacteria live and thrive in warm water (77° – 124° F) and the presence of biofilms or organic material. In building water systems, it is likely to be found when there are low levels of disinfectants (e.g., Chlorine), after construction, where there are dead-ends in the piping, in stagnant water, cooling towers, thermostatic mixing valves, decorative fountains, and in ice machines.

The bacteria can become a health concern when they grow and spread in building water systems, including:

  • Showerheads and sink faucets
  • Cooling towers (large boxes designed to maximize water evaporation for industrial buildings)
  • Hot tubs
  • Decorative fountains and water features
  • Hot water tanks and heaters
  • Large, complex plumbing systems

Legionella cause disease when the bacteria grow to a sufficient amount in small droplets and aerosols of the contaminated water. When people breathe in these small, bacteria-contaminated water droplets, they can become ill.

Legionellosis is often categorized as being community, travel, or hospital-acquired based on the type of exposure. Less common, people can become ill by accidental aspiration (inhalation) of drinking water containing Legionella.


The likelihood of getting sick depends on the concentration of Legionella within the water source, the production and dissemination of aerosols, host factors such as age and pre-existing health conditions, and the virulence of the strain of Legionella. 75–80% of reported cases are over 50 years old, and 60–70% are male.

The infective dose is unknown but can be assumed to be low for susceptible people. Illnesses have occurred after short exposures only three or more kilometers from the source of outbreaks due to the dissemination of aerosols from cooling towers. Legionnaires’ disease is not generally known to spread from person-to-person.

Risk Factors

Risk factors for community-acquired and travel-associated legionellosis include smoking, a history of heavy drinking, pulmonary-related illness, immunosuppression, and chronic respiratory or renal illnesses.

Risk factors for hospital-acquired pneumonia are recent surgery, intubation, mechanical ventilation, aspiration, presence of nasogastric tubes, and the use of respiratory-therapy equipment.

The most susceptible hosts are immunocompromised patients, including organ transplant recipients, cancer patients, and those receiving corticosteroid treatment.

Risk Management

Prevention of Legionnaires’ disease depends on applying control measures to minimize the growth of Legionella and dissemination of aerosols. Although it is not always possible to eradicate the source of infection, it is possible to reduce the risks substantially. ASHRAE Standard 188 provides the framework for owners and managers of human-occupied buildings to create and implement water management plans specific to each building and water system.

The ASHRAE Standard 188 water management program elements include:

  • Program Team
  • Describe Water System/Flow Diagrams
  • Analysis of Building Water Systems
  • Control Measures
  • Monitoring/Corrective Actions
  • Confirmation
  • Documentation

ASHRAE 188 does not explicitly require testing or provide guidance on testing protocols or parameters, but it does mandate periodic confirmation and validation of program effectiveness.

Confirmation and Validation

ASHRAE 188 compliance requires that procedures are established to confirm, both initially and on an ongoing basis, that the program controls hazardous conditions throughout the building water systems.

The Program Team shall determine whether testing for Legionella shall be performed and if testing is performed, the results will be used to validate the program. AirQuest can work with the Program Team to develop customized testing and validation protocols specific to any building’s water system.

Our industrial hygienists can provide sampling and analysis guidance covering:

  • Sampling strategy and plan development
  • Sample collection
  • Laboratory selection and analysis methods
  • Data evaluation and interpretation

Why Sample for Legionella?

Periodic monitoring for Legionella bacteria will supplement any comprehensive maintenance program and demonstrate a clear action of due diligence while ensuring program effectiveness. A proper and thorough Legionella assessment, combined with routine water testing and environmental sampling, is recommended to keep your building’s water systems (and occupants) healthy.

The benefits of a testing and validation program with AirQuest include:

  • Preventative approach
  • Proactive versus reactive sampling
  • Increased confidence in plan/program effectiveness
  • Provides a valuable resource to typical engineering-based investigation/survey team
  • Any severe outbreak that could happen would be significantly more financially detrimental to property owners than the cost of implementation of a testing and validation program.
  • Provides documented historical data to support and help protect building owners and managers against potential litigation.


“Legionnaires Disease Cause and Spread.” Centers for Disease Control and Prevention, 25 Mar. 2021, https://www.cdc.gov/legionella/about/causes-transmission.html.

“Legionellosis.” World Health Organization, 16 Feb. 2018, https://www.who.int/news-room/fact-sheets/detail/legionellosis.