Now is a really good time to focus on carbapenem-resistant bacteria. We have spent much of the past 3 years focusing on one particular virus. But now that the clinical issues linked to SARS-CoV-2 are waning for our hospital patients, the threat of carbapenem-resistance in Gram-negative bacteria comes to the fore. An excellent study with far-reaching consequences has been published from Italy. Carbapenem resistance is bad news if you have a BSI: patients with carbapenem-resistant BSI were roughly twice as likely to die as patients with carbepenem-susceptible BSI.

This study was undertaken across 19 Italian hospitals between 2018 and 2020. A total of 1276 monoclonal Gram-negative BSIs were included (polymicrobial BSIs were excluded). The prevalence of carbapenem-resistance amongst these BSIs was alarming, 304/1276 (23.8%) were KPC-producing CRE, 77/1276 (6%) MBL-producing CRE (MBLs includes NDM, VIM, and IMP carbapenemases), 61/1276 (4.8%) CRPA, and 111/1276 (8.7%) CRAB BSI. This means that only a slight majority of the cases (723/1276 (56.7%)) were carbapenem-susceptible! This is a very different picture to the UK, where <1% of invasive Klebsiella BSIs are carbapenem-resistant – but it’s not dissimilar to other regions in the south of Europe (such as Greece).

Overall, and in line with previous studies, carbapenem-resistance roughly doubled the crude 30-day mortality compared with carbapenem-susceptible BSIs. 30-day mortality was 13.7% for carbapenem-susceptible BSI, 26.6% for KPC CRE, 36.4% for MBL CRE, 32.8% for CRPA, and 43.2% for CRAB. However, this isn’t the complete picture, because patients who develop infections with carbapenem-resistant organisms are also more likely to die from other causes, so mortality findings are confounded (at least to a degree). The study team undertook a risk-adjusted multivariable analysis and concluded that the attributable mortality was 5% for KPC CRE, 35% for MBL CRE, 19% for CRPA, and 16% for CRAB. The difference between KPC CRE and MBL CRE is important, and probably driven by the broader spectrum and higher level of antimicrobial resistance associated with MBL CRE.

These findings are not surprisingly, but the both prevalence of carbapenem-resistance and the impact on mortality is stark, and should serve as a reminder to us all to focus on the prevention of antibiotic-resistant bacteria.