Diagnostic yield of BAL vs. non-invasive analysis in patients with CAP

<bold>Background:</bold> Community-acquired pneumonia (CAP) remains a significant contributor to both morbidity and mortality. Using the Swiss data from the CAPNETZ 2.0 cohort study, we analyzed the yield of microbiological analysis in patients with CAP. <bold>Methods:</bold> Adults with radiologically confirmed CAP were eligible for enrollment. The recruitment occurred at the Basel and St. Gallen study centers from 2018 to 2022. Results of microbiological analysis were analyzed. <bold>Results:</bold> A total of 229 patients (35.4% female, 98.3% hospitalized, mean age 61.7 years) were included. Blood cultures were obtained from 194 patients (84.7%), with pathogen detection observed in 6.7%. Urine antigen test for Streptococcus pneumoniae and for Legionella pneumophila were performed in 143 and 160 patients (62.4% and 69.9%) respectively, and were positive in 11.9% and 3.1%, respectively. Sputum culture was conducted in 50 patients (21.8%), with pathogen identification in 56%, most frequently S. pneumoniae (14%) and Haemophilus influenzae (10%). Sputum PCR was performed in 6 patients (2.6%) and positive in 2 patients (L. pneumophila and Mycoplasma pneumoniae). BAL cultures were performed in 140 patients (61.1%), with pathogen detection in 32.1%, most frequently P. aeruginosa (7.8%) and S. aureus (5.0%). BAL multiplex PCR was conducted in 142 patients (62.0%), with positive results in 26.1%, most frequently Rhinovirus (9.1%) and P. aeruginosa (2.8%). <bold>Discussion:</bold> Sputum culture had the highest yield of microbiological diagnosis but was performed in less than a quarter of patients. More frequent use of sputum culture and, when negative, BAL including molecular testing for respiratory viruses likely improves etiologic diagnosis in CAP.