Testing for Legionella Pneumonia in Those at Risk: Room for Improvement

lung cancer concept. doctor explaining results of lung check up from x-ray scan chest on digital tablet screen to patien
Is testing for Legionella pneumophila appropriate and could it impact treatment?

According to a study published in the journal Chest, testing for legionella was uncommon, even for patients with risk factors. Furthermore, many patients positive for legionella failed to receive empiric coverage for legionellapneumonia (LP), said investigators.

Current American Thoracic Society/Infectious Diseases Society of America (ATS/IDSA) guidelines recommend against routine Legionella pneumophila testing but do recommend patients hospitalized with community-acquired pneumonia (CAP) receive treatment that covers legionella. Investigators conducted a retrospective cohort analysis of patients eligible for testing to see whether testing had been appropriate and could have impacted treatment.

A total of 166,689 patients were eligible for testing from 2010 to 2015, according to the Premiere Healthcare Database. Of those eligible, 43,070 (25.8%) were tested and 642 (1.5%) tested positive. The mean time from admission to testing was 1.9 days.

The percentage of patients with hyponatremia and diarrhea who were not tested was 70% and 68%, respectively. Among the patients admitted to the intensive care unit (ICU), only 28% received a test. The percentage of patients presenting with pneumonia in the legionella season of June to October was 36%, but the percentage of positive tests was 70%.

Among all patients with positive tests, 495 (77%) were initially treated with adequate antibiotics. Inadequate coverage was associated with risk factors for multidrug-resistant organisms or hospital-acquired pneumonia (36.1% vs 20.0%) and longer time to test (2.4±1.7 vs 1.9±1.3 days). Those admitted to the ICU were not more likely to receive adequate coverage.

During the data period of this study, not all hospitals had easy access to urinary antigen testing (UAT) and the testing rate was relatively low at 25%, meaning risk factors or treatment effects in patients who weren’t tested may have been missed, said investigators.

Other limitations were that the impact of antibiotic choice on outcome for LP patients was not assessed and that most testing was UAT, which can detect only serogroup 1. Outpatient records were also not available and investigators couldn’t comment on patients’ prehospital course or treatment.

Investigators conclude that increased attention by clinicians toward seasonal variation in LP testing, adequate coverage for LP as a routine part of empiric antibiotic therapy, and initial testing in patients with risk factors may potentially increase detection and improve outcomes.


Allgaier J, Lagu T, Haessler S, et al. Risk factors, management, and outcomes of legionella pneumonia in a large nationally-representative sample. Chest. Published online December 19, 2020. doi:10.1016/j.chest.2020.12.013