Limited impact of colistin resistance on mortality of intensive care patients with carbapenem-resistant bacteraemia.

Background: Increasing incidence of carbapenem-resistant Gram-negative bacteraemia (CR-GNB) has triggered increased use of polymyxins, likely fuelling the emergence and spread of colistin resistance.
Aim: To estimate the excess clinical burden of colistin resistance in intensive care patients with CR-GNB.
Methods: A cohort of patients with CR-GNB during their stay in the intensive care unit (ICU) of a university hospital in Greece over a 4-year period (2020-2023) was constructed. Competing risks survival analysis was performed to estimate the burden associated with colistin resistance.
Findings: Of the 177 ICU patients with CR-GNB, 134 (76%) had colistin-resistant isolates, predominantly Acinetobacter baumannii (79%), identified by broth microdilution. Patients with colistin-resistant infection were similar to those with colistin-susceptible infection with respect to age, sex, APACHE II score, Charlson comorbidity index score, Pitt bacteraemia score, prior surgery and the occurrence of polymicrobial cultures. However, patients in the colistin-resistant group had lower risk of mortality compared with those in the colistin-susceptible group (31% vs 44%, P = 0.004 at 14 days, respectively; 46% vs 56% at 28 days, respectively; P = 0.173). Multi-variable regression analysis confirmed that colistin-resistant CR-GNB was associated with significantly lower risk of inpatient death compared with colistin-susceptible CR-GNB within 14 days [cause-specific hazard ratio (csHR) 0.53, 95% CI 0.28-1.01) and 28 days (csHR 0.55, 95% CI 0.31-0.95) of infection onset.
Conclusion: Limited impact of colistin resistance on mortality was demonstrated in a large contemporary cohort of ICU patients with CR-GNB, possibly reflecting the recent shift away from colistin-based treatment regimens.
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