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SCIENCE / MEDICINE : Warning on Legionnaire’s Disease

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Chlorine, which is normally used for sterilizing water used for drinking and in cooling systems, may not be effective against the microorganism that causes legionnaire’s disease, according to Jeannine Navratil of the Pittsburgh Department of Water. The microorganism that causes the disease is much more resistant to chlorine than other water-borne pathogens and can colonize hot water reservoirs at the end of potable water systems, she reported.

About 700 cases of legionnaire’s disease are reported to the U.S. Centers for Disease Control each year, but that number is believed to represent only a small fraction of total cases. About 15% of infections prove fatal.

The organism, Legionella pneumophila, escapes the chlorine by hiding inside certain amoebas, which form inactive cysts when stressed, such as by exposure to chlorine. These amoebas, she said, can withstand 10 times the amount of chlorine normally used to disinfect water and still support legionella growth, she said.

In many cases, she said, it may be necessary to use ultraviolet light or other disinfectants to kill the L. pneumophila.

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