The burden of hospital-acquired legionellosis in German teaching hospitals
Purpose: 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 was to quantify the incidence of these infections both nationwide and regionally (specifically in Baden-Württemberg) for university hospitals. In addition, the extent to which the drinking water systems in university hospitals are routinely tested and what measures are taken when limit values are exceeded was investigated.  Methods: We conducted a retrospective analysis of nosocomial Legionella cases over a five-year period (from 2020 to 2024) at the University Medical Center Freiburg including confirmation of hospital transmission by genomic typing. A nationwide survey was distributed to all 36 German university hospitals to collect data on the incidence of nosocomial infections and prevention strategies. Additionally, detailed information from five university hospitals in Baden-Württemberg was collected to gain regional insights into prevention measures and their costs. Results: During the five-year period at the University Medical Center Freiburg, three patients met the criteria for Legionnaires' disease and were classified as hospital-acquired cases. Two of these were subsequently confirmed by genome analysis to have been caused by nosocomial transmission. Across the country, 26 of 36 University hospitals reported a total of sixteen cases, with all reporting hospitals exceeding the regulatory Legionella limits in their water systems. There were large differences in preventive measures between these university hospitals: The number of sampling points in hospitals' drinking water system ranged from 30 and 2355, and the total of bacterial filters installed per hospital ranged from 30 to 2,200, indicating a remarkable level of prevention measures in contrast to the very low incidence of infections, even in high-risk patient populations. Conclusions: Nosocomial Legionella infections remain rare in German tertiary care hospitals, indicating a low overall risk even among vulnerable patients. The low infection burden contrasts the implementation of resource-intensive surveillance and prevention strategies in these hospitals. The considerable differences in prevention efforts, even the regional differences observed in Baden-Württemberg, underscore the need for a critical reassessment of current practices. Optimizing the use of resources without compromising patient safety is an essential prerequisite for effective and efficient infection control.