Background Patients with renal impairment have altered immunity, which might cause vulnerability to specific pathogens and worsen pneumonia-related outcomes. Nonetheless, the microbiological features of pneumonia in patients with decreased renal function remain unknown. Methods Therefore, we conducted a retrospective cohort study enrolling adult patients hospitalized with pneumonia to assess this knowledge gap. The baseline estimated glomerular filtration rate (eGFR) and first sputum microbiology during hospitalization were used for statistical analyses. Results Overall, 1554 patients hospitalized with pneumonia (mean age, 76.1 ± 16.7) were included, and 162 patients had died at the end of hospitalization. The cutoff eGFR value predicting mortality was <55 mL/min/1.73 m 2 , which defined decreased renal function in this study. Patients with decreased renal function demonstrated a significantly higher risk of fungi and Staphylococcus aureus (S. aureus) infection. On the other hand, this group of patients showed significantly higher neutrophil-to-lymphocyte ratio (NLR), which associated with higher mortality. Additionally, patients with S. aureus had a significantly lower eGFR, lymphocyte count and a higher NLR. Conclusions These findings suggested the altered immunity and vulnerability to S. aureus infection in patients with decreased renal function, which may be the underlying cause of worse outcomes of pneumonia in this group of patients.
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