2018 Volume 33 Issue 5 Pages 193-202
In September 2013, an outbreak of hospital-acquired Legionella pneumonia caused by the L. pneumophila serogroup 1 was confirmed. An investigation resulted in suspecting the infection source to be a hot water-supply system because the banding pattern on pulse-field gel electrophoresis of Legionella DNA from the hot water in patients' rooms matched with that of the sputum sample collected from patients. In addition, the investigation of the contaminated hot water-supply system detected L. pneumophila SG 1 from one of the mixed-water faucets. As disinfection measures, after disinfection, hot water was continuously discharged to prevent the temperature of the hot water in the distribution pipe from decreasing. Moreover, unnecessary pipes were removed, which successfully eliminated the bacteria. However, the L. pneumophila SG 1 contamination was detected again from the 40°C-mixed water, leading to investigation at 92 places. Consequently, the same bacteria were detected at 23 places, and the contamination of the water-supply system was confirmed. As disinfection measures of the water supply system, sodium hypochlorite was continuously added to the water-receiving tank to maintain the free residual chlorine concentration at ≥0.87 mg/L at the mixed-water faucets. Furthermore, water was discharged from the most distal mixed-water faucet for 6 minutes and from all hospital room washbasin faucets for 1 minute every day. These measures increased the free residual chlorine concentration to an average of 0.81 mg/L (P<0.01), and the detection rate of the same bacteria decreased from 13.6% to 0.4% (P<0.01), confirming the efficacy of the measures. This study suggests that an investigation should be conducted considering the possibility that the water-supply system may be the source of contamination when Legionella contamination in the hot water-supply system is detected.
