Differences in severity of bacteremia caused by hypermucoviscous and non- hypermucoviscous Klebsiella pneumoniae.

BACKGROUND: Klebsiella pneumoniae strains pose a significant threat to public health. Currently, it is inconclusive as to whether hypermucoviscous K. pneumoniae (hmKp; this phenotype has been semi-quantitatively defined by a positive "string test") bacteremia is clinically more severe than non-hmKp bacteremia. Hence, we aimed to conduct this systematic review and meta-analysis to draw some conclusions on hypermucoviscosity and bacteremia.

METHODS: We searched PubMed and Web of Science databases for all relevant publications from January 2000 to March 2022. The outcome measures were mortality rate and abscess formation.

RESULTS: We included 14 observational studies in this systematic review, comprising a total of 3,092 patients with K. pneumoniae bacteremia, including 746 (24.1%) patients with hmKp strains. The meta-analysis showed that hmKp bacteremia did not account for a statistically significant increase in the incidence of all-cause mortality compared to non-hmKp bacteremia (pooled hazard ratio (HR), 1.30 [95% CI: 0.79, 2.12], P = 0.30). However, hmKp bacteremia was associated with a statistically significant increase in the incidence of abscess formation compared to non-hmKp bacteremia (pooled odds ratio (OR), 7.74 [95% CI: 4.96, 12.06], P<0.00001).

CONCLUSIONS: Although the mortality may not be dependent on the causative agent, we reaffirm the importance of the string test to detect hmKp. Therefore, there is a need for prudent management, especially for bacteremia patients with string-test-positive K. pneumoniae, that should include investigations for liver abscess and/or metastatic spread, and measures for an early and proper source control as it can improve the prognosis.