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The CDC is warning that using nonsterile ice to cool saline-filled syringes for bronchoalveolar lavage creates a risk of Legionnaire's disease.

The warning arises from what the agency is calling a "pseudo-outbreak" of Legionnaire's at an Arizona medical center in mid-2008, in which cultures from four patients tested positive for Legionella pneumophila.

None of the four patients had a fever or a clinical course consistent with the disease, the agency said in the Aug. 13 issue of Morbidity and Mortality Weekly Report.

Instead, investigation found that nonsterile ice was the most likely source of the pathogen, the CDC said.

The report is the second "pseudo-outbreak" of Legionnaire's in recent years. In 2007, a similar event occurred among 13 patients whose bronchoalveolar lavage specimens were contaminated by nonsterile ice for saline cooling during bronchoscopies.

In that event, though, one case of a lower respiratory tract infection was blamed on the pathogen, the agency said, "demonstrating that the use of nonsterile ice during bronchoscopies creates a risk for Legionella infection."

The CDC said that the bacteria grow between 77°F (25°C) and 108°F (42°C), which "might have created the perception that ice could not support Legionella growth."

The reality: although low temperatures slow the growth of the bacteria, Legionella can remain alive in ice for some time, the CDC said.

The potable water supply of the Arizona center had been colonized by Legionella between February and July, 2008, the CDC said, and the system supplied water to the ice machines.

In July of that year, endoscopic technicians began using cold saline flushes to control bleeding in patients having bronchoalveolar lavage. Ice for the cooling was supplied by a machine in a nearby nursing station, or by a backup machine in a kitchen.

L. pneumophila serogroup 8 -- the serogroup detected in cultures from the four patients -- was found in both ice machines. A second serogroup was also found in the backup machine.

The four isolates obtained from the patients had sequence-based typing patterns that were identical to those of the samples from both ice machines.

The investigators couldn't find any possible other source of contamination, the agency said.

One immediate implication of the event, the CDC said, is that "ice machines can be reservoirs for Legionella contamination and should be disinfected."

At the same time, the agency said, if sterile ice is not available, clinicians should be careful to ensure that nonsterile ice does not come in direct contact with equipment or patient specimens.