Impact of positive legionella urinary antigen test on patient management and improvement of antibiotic use

Aim: To assess the incidence of legionella infection over a 27 month period at a large university hospital. Material and Methods: The present retrospective cohort study enrolled patients with legionellosis, defined as those presenting a positive urinary antigen for legionella together with a medical history, clinical findings, and radiological findings consistent with pneumonia. These patients were evaluated to determine the relation between their test results and changes in treatment modalities. A control group of patients with pneumonia but a negative urinary antigen test for legionella were also analysed. Results: Twenty seven of 792 assessed patients tested positive for legionella. In 22 of these patients, legionella active antibiotics were administered empirically. In seven patients, the test results prompted a legionella specific treatment, whereas in 12 cases, non-specific antibiotics were stopped within 24 hours. Overall, treatment was altered in more than half of the patients as a result of the test results. Conclusions: The urinary antigen may have a direct impact on clinical management of pulmonary legionellosis. However, patient comorbidities and individual clinical judgment are still important for determining the best treatment to be given in each individual case.