Influence of Antibiotics on the Detection of Bacteria by Culture-Based and Culture-Independent Diagnostic Tests in Patients Hospitalized With Community-Acquired Pneumonia

Background Specimens collected after antibiotic exposure may reduce culture-based bacterial detections. The impact on culture-independent diagnostic tests is unclear. We assessed the effect of antibiotic exposure on both of these test results among patients hospitalized with community-acquired pneumonia (CAP). Methods Culture-based bacterial testing included blood cultures and high-quality sputum or endotracheal tube (ET) aspirates; culture-independent testing included urinary antigen testing (adults) for Streptococcus pneumoniae and Legionella pneumophila and polymerase chain reaction (PCR) on nasopharyngeal and oropharyngeal (NP/OP) swabs for Mycoplasma pneumoniae and Chlamydia pneumoniae. The proportion of bacterial detections was compared between specimens collected before and after either any antibiotic exposure (prehospital and/or inpatient) or only prehospital antibiotics and increasing time after initiation of inpatient antibiotics. Results Of 4678 CAP patients, 4383 (94%) received antibiotics: 3712 (85%) only inpatient, 642 (15%) both inpatient and prehospital, and 29 ( Conclusions Bacteria were less frequently detected in culture-based tests collected after antibiotics and in culture-independent tests that had longer intervals between antibiotic exposure and specimen collection. Bacterial yield could improve if specimens were collected promptly, preferably before antibiotics, providing data for improved antibiotic selection.