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 was constructed 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). Competing risks survival analysis was performed to estimate the burden associated with colistin resistance.

Findings

In 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 with respect to age, sex, APACHE II score, Charlson comorbidity index, Pitt bacteraemia score, prior surgery and the occurrence of polymicrobial cultures. However, patients in the colistin resistant group had lower mortality risk compared to the colistin susceptible (31% vs. 44%, P = 0.004 at 14 days; 46% vs. 56% at 28 days, P = 0.173; respectively). Multivariable regression analysis confirmed that colistin resistant CR-GNB was associated with significantly lower hazard of inpatient death compared to colistin susceptible infection at 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.