Comparison of Bacterial and Clinical Features of Klebsiella pneumoniae and Klebsiella oxytoca Bloodstream Infections: Experience at a Tertiary Hospital in Japan

Background: Klebsiella pneumoniae (KP) and Klebsiella oxytoca(KO) are two major Klebsiella species that cause various infections including bloodstream infection (BSI). Multidrug resistance among Klebsiella species has rapidly emerged and is associated with high rates of morbidity and mortality. However, few reports describe the differences in bacterial and clinical characteristics of BSI caused by these two species. Thus, this study aimed to describe and compare the clinical characteristics of BSI caused by KP and KO.

Methods: We conducted a retrospective, single-center cohort study of KP and KO BSI at a tertiary hospital with 917 beds in Japan. All episodes of KP or KO BSI between January 2013 and December 2015 were identified from our laboratory database. We excluded cases in which KP and KO were simultaneously detected from blood cultures. We examined demographic and clinical data of the patients and in vitro susceptibility profiles of the isolates to compare the characteristics of BSI caused by KP and KO.

Results: A total of 334 cases were identified; 268 (80.2%) had KP BSI and 66 (19.8%) had KO BSI. There was no significant difference in sex, age, the rate of community-onset bacteremia, or burden of comorbidities between KP and KO BSI. Biliary tract infection was less frequently the underlying source of KP BSI compared with KO BSI (37.3% in KP vs. 59.1% in KO, p=0.014), while pneumonia was significantly a more frequent source of KP BSI than KO BSI (6.0% in KP vs. 0% in KO, p=0.047). The prevalence of extended-spectrum beta-lactamase (ESBLs) producing strains was low in both groups (4.5% in KP and 6.1% in KO). Neither Klebsiella pneumoniae carbapenemase (KPC) producing strains nor metallo-beta-lactamase (MBL) producing strains were identified. The overall 30-day mortality rate was not significantly different between the two groups (19.4% in KP vs. 12.1% in KO, p=0.21).

Conclusion: KO BSI, compared with KP BSI, was more frequently associated with biliary tract infection and rarely originated from pneumonia. Multidrug-resistant strains remained infrequent in our cohort.