Background. Community-acquired pneumonia caused by Klebsiella pneumoniae is a rapidly progressive and severe form of pneumonia that generally leads to poor outcomes. However, the clinical features and outcomes of severe K. pneumoniae pneumonia (KPP) have not yet been prospectively validated using adequate control groups. Methods. A prospective cohort study was conducted using adult patients diagnosed with KPP or Streptococcus pneumoniae pneumonia (SPP) who were admitted to a 28-bed medical

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... sive care unit (ICU) in a 2,700-bed tertiary care hospital between January 2010 and February 2016. The clinical manifestations, laboratory characteristics, radiographic findings, and outcomes were compared between the KPP and SPP groups. Results. One hundred and eighty-five patients (91 severe KPP patients and 94 severe SPP patients) were included for analysis. Alcoholism was more common in the KPP group than in the SPP group (12.1% vs 3.2%, P = 0.02). Concomitant respiratory viral coinfections were significantly less frequent in the KPP group than in the SPP group (17.6% vs 41.5%, P < 0.001). The presence of septic shock (72.5% vs 67.0%, P = 0.42) and the mean APACHE II score (25.1 vs 25.8, P = 0.80) at the time of ICU admission did not differ between the groups. Both groups commonly demonstrated multiple lobe involvement (78.0% vs 87.2%, P = 0.10). Other clinical manifestations, laboratory findings, and radiologic findings did not significantly differ between the groups. Although the 28-day mortality rate (25.3% vs 22.3%, P = 0.64) was similar between the groups, the 60-day mortality rate (42.9% vs 28.8%, P = 0.045) and the 90-day mortality rate (46.2% vs 29.8%, P = 0.02) were significantly higher in the KPP group than in the SPP group (P = 0.037 by a log-rank test, Figure 1 ). Conclusion. The overall epidemiological and clinical characteristics of severe KPP patients who were admitted to ICU were comparable with those of severe SPP patients. However, severe KPP patients exhibited poorer clinical outcomes than severe SPP patients.