Legionella Species and Their Risk to Humans

Bacteria of the genus Legionella cause Legionnaires’ disease and Pontiac fever, and, more rarely, extrapulmonary infections, collectively referred to as legionellosis. According to the CDC, there are at least 60 different species of Legionella, most of which are considered to be pathogenic. However, the majority of disease is caused by Legionella pneumophila with 90% of Legionella infections in humans are caused by Legionella pneumophila.

19 Legionella species have been documented as human pathogens on the basis of their isolation from clinical material according to the article, “Infection due to Legionella species other than L. pneumophila.”

The remaining non-pneumophila species are found in water and soil and are considered non-pathogenic until shown to cause disease. Of the CDC reported cases, less than 5% are attributed to non-pathogenic species.

The CDC also states that the rates of reported cases of Legionnaires’ disease continue to rise in the United States. While nearly 10,000 cases were reported in 2018, this number may underestimate true incidence because Legionnaires’ disease is likely underdiagnosed. The study entitle “Estimate of burden and direct healthcare cost of infectious waterborne disease in the United States” stated that the true number of Legionnaires’ disease cases may be 1.8–2.7 times higher than what is reported.

Given that the presence of Legionella may be underdiagnosed, the importance of testing for Legionella in your facility on a regular basis cannot be overstated. A Legionella water management plan helps you to identify and treat Legionella before it creates real harm to your facility’s visitors in the form of Legionnaires Disease.

Below is a list of many of the Legionella species:

For more information about Legionella and its risk to your facility, contact Legionella Control Systems.