KPC vs MBL Prevalence in the United States
KPC (Klebsiella pneumoniae carbapenemase) is significantly more common than MBL (metallo-beta-lactamase) in the United States, with KPC representing the predominant carbapenemase mechanism among carbapenem-resistant Enterobacterales. 1, 2
Epidemiological Evidence
KPC remains the most common carbapenemase globally and in the United States, accounting for 47.4% of meropenem-resistant Enterobacterales in multicentre surveillance studies, while MBLs represent only 20.6% of carbapenem-resistant isolates. 3, 1 This nearly 2.5-fold difference in prevalence makes KPC the primary carbapenemase threat in U.S. healthcare facilities.
Historical Context and Geographic Distribution
- KPC-producing bacteria were first confined to outbreaks in the northeastern United States in the early 2000s, but have since spread throughout the entire country. 4
- The CDC documented a dramatic rise in carbapenem-resistant K. pneumoniae (CRKP) from fewer than 1% of all Klebsiella isolates in 2000 to 8% by 2007, with KPC being the predominant mechanism. 2
- KPC-producing organisms are no longer limited to K. pneumoniae and now affect an increasingly wide range of Gram-negative bacteria across U.S. healthcare settings. 4, 5
Clinical Implications of This Prevalence Pattern
Treatment Selection Based on U.S. Epidemiology
For empiric therapy of suspected carbapenem-resistant Enterobacterales infections in the United States, clinicians should prioritize coverage for KPC producers using ceftazidime/avibactam or meropenem/vaborbactam as first-line agents. 1 These agents have excellent activity against KPC but are ineffective against MBL producers. 1
Critical Diagnostic Considerations
- Rapid carbapenemase testing to identify the specific enzyme family (KPC vs MBL) is essential because treatment efficacy depends entirely on the carbapenemase type present. 3, 1
- KPC-producing bacteria are often misidentified by routine microbiological susceptibility testing and may be incorrectly reported as sensitive to carbapenems. 4
- Resistance to ertapenem is common in KPC producers and serves as a better indicator of KPC presence than resistance to other carbapenems. 4
Important Caveats and Pitfalls
Geographic Variation Within the United States
While KPC predominates nationally, local epidemiology can vary significantly between healthcare facilities and regions. 3 Institutions should maintain surveillance data on their specific carbapenemase distribution patterns to guide empiric therapy decisions.
Emerging MBL Threats
Although MBLs remain less common in the United States compared to KPC, MBL-producing strains (particularly NDM, VIM, and IMP types) are increasingly detected and represent a growing concern. 3, 1 MBLs are particularly problematic because they hydrolyze all beta-lactam antibiotics except aztreonam and cannot be inhibited by classic serine beta-lactamase inhibitors like avibactam. 1
Treatment Failures with Wrong Assumptions
Do not assume all carbapenem-resistant bacteria have KPC - using ceftazidime/avibactam monotherapy for an unrecognized MBL producer will result in treatment failure. 1 For MBL producers, the required regimen is ceftazidime/avibactam PLUS aztreonam or cefiderocol as an alternative. 1
Infection Control Implications
All acute care facilities must implement aggressive infection control strategies including contact precautions for all patients with carbapenem-resistant Enterobacterales, regardless of whether KPC or MBL is the mechanism. 2 The carbapenemase genes are carried on mobile genetic elements that facilitate rapid dissemination between bacterial species and across healthcare facilities. 2