It’s common to find other Legionella species in your water. As previously mentioned, the Legionella family is a big family with 58 species that exist in soil and water. When you find other Legionella species does that mean Legionella pneumophila serogroup 1 is also present?

An often cited 2006 French study attempts to make the case that after eradicating L. anisa by thermal shock treatment Legionella pneumophila serogroup 1 (LP1) appeared and that L. anisa had “masked” LP1. The authors assert that system-wide disinfection is required to reveal LP1 and that the presence of the non-pneumophila species was a predictor of the presence of the more dangerous Legionella pneumophila serogroup 1.

No other studies support their claim that finding one Legionella species predicts the presence or absence of LP1. While it’s true that multiple serogroups and even species can colonize a water system, we aren’t aware of any study that has statistically correlated the presence of a non-pneumophila species as predictive of the presence of LP1.  

The ability of a laboratory to detect some non-pneumophila Legionella species is dependent upon the methods and culture media used by the laboratory. For example, some species won’t grow in the presence of glycine–a common additive in Legionella selective media used to isolate Legionella from the environment.

Even so, based on this claim French researchers concluded that action should be taken to “eradicate all Legionella contamination.”

In contrast, all studies show that LP1 is the primary cause for disease. While non-pneumophila species have caused illness on rare occasions, to conduct a system-wide disinfection when only non-pneumophila species, such as L. anisa, are isolated is a time-consuming and costly proposition backed by very little evidence to support such an action.

To better illustrate, take a recent example. During an investigation of a facility for a suspected case of Legionnaires’ disease due to L. pneumophila serogroup 1, the testing of the facility only revealed the presence of Legionella feelei. No link could be made between the illness caused by L. pneumophila serogroup 1 and the facility. Despite this, the health department, citing CDC guidance, insisted on restricting admissions, restricting showering, use of bottled water and multiple shock chlorine treatments of the water system until all cultures were zero. The impact of these measures on the patients, staff and operation of this facility caused hardship and were extremely expensive.

In our opinion, all of these precautions were unnecessary and could have been lifted when environmental testing failed to show the presence of L. pneumophila serogroup 1.