Risk factors and the resistance mechanisms involved in mutation in critically ill patients.

Background: The objective of this study was to determine the main risk factors of mutation as well as the mechanisms of acquired resistance.

Methods: We conducted a 2-year prospective study in patients who were carriers of a strain and who had been admitted to a medical/surgical ICU.

Results: Of the 153 patients who were included, 34 had a mutation in their strain. In a multivariate analysis, a duration of ventilation > 24 days was a risk factor for mutation (risk ratio 4.29; CI 95% 1.94-9.49) while initial resistance was a protective factor (RR 0.36; CI 95% 0.18-0.71). In a univariate analysis, exposure of to ceftazidime was associated with an over-production of AmpC cephalosporinase and exposure to meropenem was associated with impermeability. A segmentation method based on the duration of ventilation (> 24 days), initial resistance, and exposure of strains to ceftazidime made it possible to predict at 83% the occurrence of mutation.

Conclusion: The duration of ventilation and the presence of resistance as soon as is identified are predictive factors of mutation in ICU patients.