Reduction in Legionella pneumophila through Heat Flushing Followed by Continuous Supplemental Chlorination of Hospital Hot Water

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Abstract
An increase in endemic rate of nosocomial Legionella pneumophila pneumonia prompted an investigation that revealed 16.2% (12/74) of patient care hot-water sites surveyed were culturepositive for L. pneumophila. No positive cultures were recovered from cooling towers, air intakes, or construction areas. Heat flushing of hospital hot-water outlets to temperatures >60°C for 30 min achieved a 66% reduction in positive Legionella cultures. After 4 1/2 months, different serotypes recurred in previously eradicated areas and there were new positive cultures. Continuous supplemental chlorination of the hot-water system (2 parts per million [ppm]) significantly reduced the number of culture-positive samples from 37.4%(43/115) to 7.0%(8/115) after 6 weeks (P < .005). Of 30 sites surveyed 6 months after hot-water chlorination, 67% (20) were still culturenegative. Of those positive, 70% had ⩽150 L. pneumophila/ml and 90% were from bathtubs. Adverse effects of chlorination on users and plumbing have not been seen. There have been no definite cases of nosocomial L. pneumophila in areas served by supplemental chlorine during the first 17 months of the chlorination project. Technology allowing tighter regulation of chlorine and use of silicates to control corrosion have made continuous hot-water chlorination a safe and effective option in Legionella control.