Early Testing for Legionella Improves Pneumonia Care

Legionnaires’ disease, or legionellosis, is a severe form of pneumonia caused by Legionella bacteria. While the disease can be treated with antibiotics, it remains fatal in approximately 5-10% of cases. The disease has seen a continuous rise in reported cases in Switzerland over the past decade with 641 reported cases in 2023. The bacteria thrive in man-made water systems — such as showers, fountains, cooling towers and car washes.

A new study led by Swiss TPH now analysed data from 204 cases of Legionnaires’ disease treated at 20 hospitals across Switzerland between 2022 and 2024. While current Swiss and European guidelines recommend routine Legionella testing in all hospitalised pneumonia patients, the clinical benefits of this approach had not been systematically assessed until now.

“Our findings provide clear evidence that microbiological testing can improve patient care,” said Melina Bigler, first author and PhD candidate at Swiss TPH. “Timely testing led to a reduced use of broad-spectrum antibiotics. This not only minimises antibiotic-related side effects in patients but is also a critical step in combating antimicrobial resistance.”

The study also found that more than one-third of patients were treated with antibiotics for longer than recommended by current clinical guidelines — a median of four days too long — even after reaching clinical stability. ”The results are highly relevant for clinical practice,” said Werner Albrich, senior author of the study and Senior Attending Physician at the Cantonal Hospital St. Gallen. “They suggest that we can safely reduce treatment durations in stable patients with Legionnaires’ disease”.

The researchers hope that the study will contribute to the national efforts under the Strategy on Antibiotic Resistance, which aims to ensure responsible antibiotic use, limit resistance, and protect public health through evidence-based interventions.

“It is now essential that we continue raising awareness among physicians that shorter courses should be standard in clinically stable cases and that antibiotics be prescribed more cautiously after hospital discharge,” said Daniel Mäusezahl, senior author of the study and group leader at Swiss TPH. “This way, we can improve health outcomes, limit side effects, and significantly reduce resistance pressure — a win for both patients and public health.”

The study was conducted as part of the SwissLEGIO project, a national research initiative led by Swiss TPH in partnership with Federal Office of Public Health (FOPH), the National Reference Centre for Legionella (NRCL), the SwissLEGIO Hospital Network and several academic partners.