Misting System Blamed for 100 Cases of Pontiac Fever

Misting systems have become popular in dry climate regions, emitting a fine spray along walkways of major hotels, at outdoor restaurants, and around home patios. The devices provide conditions that seem perfect for legionellae growth and transmission: small plastic tubing (conducive to biofilm growth) that's typically exposed to sunlight, stagnation while the system's off at night, low flow rates, and efficient aerosolization of small water particles. 

A misting system used for the decor at a rainforest-theme restaurant was recently blamed for 100 cases of Pontiac fever (reported in The Tennessean, Friday, 10 May 2002), a flu like illness caused by Legionella. 

The U.S. Centers for Disease Control and Prevention confirmed that 100 individuals contracted Pontiac fever after dining at the restaurant on or around 19 April 2002. The water misting system was suspected after food poisoning and person-to-person transmission were both ruled out. 

The CDC confirmed that legionellae were found in the misting system, but the news report did not state whether the Legionella strains matched those found in patients. The health department shut down the restaurant's misting system, but agreed that it could be turned back on after disinfection. 

The department plans to continue routine testing of the chlorine residual. According to the restaurant chief executive officer, the owners had been flushing the water system with chlorine, so they were puzzled that it did not work. 

Note: Chlorine may not be effective in this system because small plastic tubing is very conducive to biofilm growth. At low levels of 1-2 ppm, chlorine will not sufficiently penetrate biofilm.-mrf .