The burden of hospital-acquired legionellosis in German teaching hospitals

Legionella pneumophila is a recognized cause of hospital-acquired pneumonia particularly in immunocompromised patients. Significant resources are dedicated to the monitoring and control of Legionella contamination in hospital water systems. However, the actual risk of nosocomial Legionella infections in German university hospitals, which represent large tertiary care institutions, remains poorly defined. The aim of this study was to quantify the incidence of nosocomial legionellosis in German university hospitals. In addition, the extent of routine testing of hospital drinking water systems and preventive measures implemented on legal grounds was investigated.

We conducted a retrospective analysis of nosocomial Legionella cases over a five-year period (2020-2024) at the University Medical Center Freiburg (UMCFR), including in-depth genomic typing. We distributed a survey to all 36 German university hospitals to collect data on the incidence of nosocomial infections and prevention strategies. We collected comprehensive data on preventive measures on a regional level among university hospitals in Baden-Württemberg.

Over a five-year period at UMCFR, three patients met the criteria for nosocomial Legionnaires' disease (LD). In two of these cases, we were able to confirm transmission through the hospital's drinking water system by genome analysis. Nationwide, 26 of 36 University hospitals reported a total of sixteen cases. All hospitals documented abnormal parametric values (≥ 100 CFU/ml) in their drinking water systems at least once per year. Preventive measures varied widely: the number of sampling points ranged from 30 to 2355, and the number of point-of-use water filters from 30 to 2,200 per hospital. Despite this, incidence of LD remained very low.

Nosocomial Legionella infections are rare in German tertiary care hospitals. However, the impact of intensive prevention measures on the incidence rates of nosocomial Legionella infections remains unclear. Therefore, current practices should be re-evaluated to optimize the use of resources without compromising patient safety.