Background: Nosocomial legionellosis is associated with high mortality. Here, we present the results of an epidemiological investigation and the control measures undertaken for a case of nosocomial Legionella pneumonia at a pediatric hematopoietic stem cell transplantation (HSCT) unit.
Methods: A 22-month-old boy developed nosocomial Legionella pneumonia while at a pediatric HSCT unit. A multidisciplinary team conducted an environmental assessment of the hospital water system and collected water and swab samples from faucets and shower heads from the index patient rooms and nurse stations for Legionella culture.
Results: Legionella was isolated from two swab samples and four water samples out of a total of 24 environmental samples. Follow-up cultures were conducted after replacing the faucets or shower heads which tested positive on Legionella cultures, and point-of-use filters were additionally installed on the sites where Legionella were still isolated. When the water temperature was measured in 20 patient areas, the hot water from the four areas was 50°C or less. Based on the results of the investigation, several interventions including water temperature increase (60°C or higher), flushing out hot water in all patient rooms monthly, cleaning and disinfecting faucets and shower heads monthly, and expanding sampling sites for surveillance were implemented. After the implementation of the control measures, no cases of nosocomial legionellosis occurred, and Legionella was not detected in environmental samples.
Conclusion: Conducting multidisciplinary collaboration and investigation, even for a single nosocomial legionellosis, is important to identify the source and to prevent further transmission. Hospitals should maintain comprehensive water management programs and ensure that control measures are implemented through continuous monitoring.

Keywords: Infection control, Legionella, Pneumonia, Surveillance