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Fast Facts about Legionella:

  • Legionellacan cause Legionnaires’ disease or Pontiac fever, collectively known as legionellosis.
  • The bacterium was named after an outbreak in 1976, when many people who went to a Philadelphia convention of the American Legion got sick with pneumonia (lung infection).
  • About 6,000 cases of Legionnaires’ disease were reported in the United States in 2015. However, because Legionnaires’ disease is likely underdiagnosed, this number may underestimate the true incidence.
  • About one out of every 10 people who get sick from Legionnaires’ disease will die.
  • People can get Legionnaires’ disease or Pontiac fever when they breathe in small droplets of water in the air that contain Legionella.
  • In general, people do not spread Legionnaires’ disease to other people. However, this may be possible in rare cases.
  • Legionellais found naturally in fresh water environments, like lakes and streams. It can become a health concern when it grows and spreads in human-made water systems.
  • Keeping Legionellaout of water systems in buildings is key to preventing infection.


Illness caused by the gram-negative bacteria in the genus Legionella is referred to as legionellosis. Legionellosis consists of two distinct clinical syndromes, Legionnaires’ disease and Pontiac fever.  Legionnaires’ disease is characterized by pneumonia whereas Pontiac fever is a self-limiting, nonpneumonic, influenza-like illness. Inhalation of aerosols containing the bacterium is presumed to be the primary means of acquiring legionellosis.  Aerosolized waters from cooling towers, evaporative condensers, showers, and humidifiers have been identified as sources of infection.  Legionella species have been recovered from a wide variety of domestic water systems and are ubiquitous in freshwater environments. Although once considered transient contaminants of natural and domestic waters, legionellae are now known to be free-living organisms surviving as natural components of freshwater ecosystems.  Domestic systems are complex environments in which concentrations of legionellae can fluctuate considerably depending upon water temperature, biocide levels, and presence of natural hosts (i.e. protozoa) for legionellae to parasitize.


Chem, Inc. follows the U.S Department of Health and Human Services’ CDC guidelines and methods for the recovery and isolation of Legionella from the Environment. The testing method that we use is considered the “Gold Standard” when it comes to testing for Legionella. The method provides accurate results, while minimizing the risk of false positives.


What is the CDC’s ELITE program?

Although Legionella lives in a wide variety of freshwater habitats, it can be difficult to isolate. CDC’s Environmental Legionella Isolation Techniques Evaluation (ELITE) Program was created as a way for laboratories to test their Legionellaisolation techniques against standardized samples.


Why does the CDC offer the ELITE program?

The ELITE Program certifies labs in the isolation of Legionella from water samples. Labs that are proficient in Legionella isolation are listed on the ELITE Members List as a service for the general public. Labs that perform adequately receive a Certificate of Proficiency that indicates that the lab’s procedures are consistent with federal recommendations and that they meet or exceed typical industry standards for recovery of Legionella.


Serogroups of Legionella

Legionella pneumophila is the species responsible for ≈90% of human cases of infection. L. pneumophila is divided into 15 serogroups, among which serogroup 1 is the most prevalent disease-causing variant. In contrast, rare cases are caused by other serogroups.


Our testing allows a separate identification of Legionella pneumophilia serogroup 1, and Legionella pneumophiliaserogroups 2-14 and detection of seven other Legionella species which have been implicated in human disease.

Seven other species detected:

  1. longbeachae 1 and 2
  2. bozemanii 1 and 2
  3. dumoffii
  4. gormanii
  5. jordanis
  6. micdadei
  7. anisa


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