Changes In Lower Respiratory Tract Bacterial Isolates In ICU Patients Before and After the COVID-19 Pandemic.

To compare the distribution of bacterial pathogens isolated from lower respiratory tract specimens in COVID-19-negative intensive care unit patients before and after the COVID-19 pandemic, culture results from patients admitted to a university hospital chest diseases intensive care unit were retrospectively analyzed. Patients without clinical or radiological suspicion of COVID-19 and with negative PCR results were included and classified as pre-COVID-19 or post-COVID-19 based on March 2020. Specimens were cultured on 5% sheep blood agar, eosin methylene blue agar, and chocolate agar, and evaluated after 24-48 h incubation at 37 °C. Only dominant microorganisms demonstrating growth in at least the second streaking sector were considered clinically significant. A total of 1,665 patients were included, with microbial growth detected in 48.9% of samples, the majority originating from the pre-COVID-19 period. Acinetobacter baumannii was the most frequently isolated organism in both periods. Logistic regression analysis showed reduced detection rates of Klebsiella pneumoniae, Pseudomonas aeruginosa, and Staphylococcus aureus (odds ratio ≈0.3), and Escherichia coli (odds ratio ≈0.4) in the post-COVID-19 period. Mortality rates were also lower in the post-COVID-19 period, although no significant difference in discharge type was observed. Overall pathogen diversity remained similar across periods; however, decreases in selected bacterial detections were observed following the onset of the pandemic. These findings may reflect changes in infection control practices during the pandemic period, although causality cannot be established due to the retrospective study design and absence of direct measurements of contributing factors.