Legionella anisa is in our hospital water supply. Should we disinfect?

Legionella anisa was found in a surprising number of the distal water sites in our hospital. No cases of Legionnaires’ disease have ever been detected, although we do not have Legionella culture available as a diagnostic test. Since the urinary antigen does not identify L. anisa, should we disinfect our water supply?

The majority (>90%) of cases of Legionnaires’ disease reported in the  U.S. are caused by Legionella pneumophila. L. anisa is included in the “other species” group which is less than 10% for all other Legionella species. There are 48 named species of Legionella, with approximately half having been implicated in human disease.

L. anisa is frequently isolated from environmental specimens but very rarely causes disease.  Disease caused by other Legionella species, like L. anisa, occurs almost exclusively in immunocompromised individuals. Only a handful of cases attributed to L. anisa  have been reported. We consider this species as nonpathogenic (Yu, J Infect Chemother 2004, Stout, in press). And, we would NOT disinfect your water supply.