Influence of antibiotic pressure on multi-drug resistant colonisation in critically ill patients.

Background: The aim of this study is to evaluate the risk factors for colonisation by multidrug resistant (MDR) in a critical care unit and the relationship between colonisation and the antibiotic pressure exerted by the antimicrobial treatments received by patients.

Methods: A prospective observational was designed. Patients admitted for more than 48 h to an intensive care unit were included. Samples for surveillance cultures were obtained from all the patients upon admission and once a week. The association between risk factors and colonisation by MDR was determined by logistic regression. A Cox regression model was used to evaluate the effect of the use of antimicrobials on the colonisation rate. An ARMIA model was used to investigate the association between the incidence of colonisation by MDR strains and the global consumption of antimicrobials in the unit.

Results: One thousand seven hundred twenty-five patients were included, from which 308 (17.9%) were positive for MDR . In the multivariate analysis, hospitalisation for longer than 7 days together with respiratory infection and administration of any antibiotic was associated with increased MR colonisation. Patients who received antibiotics for more than 48 h were colonised earlier than patients who did not receive antibiotic treatment [HR: 2.16 (95%CI:1.55-3.03)]. The ARIMA model found a significant association between the monthly colonisation rate for MR and the consumption of cephalosporins and carbapenems in the previous month.

Conclusion: Individual antibiotic administration and the global antibiotic pressure of cephalosporins and carbapenems are associated to an increased colonisation by MDR strains.