Risk factors of infection and molecular typing in ICU colonized patients with Enterobacter aerogenes

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Objectives

To identify risk factors for Enterobacter aerogenes (Ea) infection in colonized intensive care patients and compare by Pulsed-Field Gel Electrophoresis (PFGE) infection strains to colonization strains.

Methods

During a prospective 8 month period, prescription order of perineal swabs has been undertaken to all ICU patients hospitalized more than 48 h on the admission day, discharge and on a weekly basis. The following risk factors were studied by univariate and multivariate analyses: age, sex, underlying pathologies, antibiotic and corticoid therapies, SAPS II score, intravascular and urinary catheters, surgical drain, nasogastric tube, use of mechanical ventilation, bronchoscopy, length of ICU stay, length between hospital and ICU admission (H/ICU) and mortality rate. Antimicrobial susceptibility and clonal analysis by PFGE were performed in colonized and infected groups.

Results

204 patients were included: 170 without Ea colonization/infection (83.3%), 24 colonized (11.8%) and 10 infected (4.9%). The Ea infection in colonized patients was associated with younger age: respectively 76.5 years in colonized and 63.5 years in infected patients (P= 0.039); higher ICU stay (9 days versus 31 days; P= 0.007) mechanical ventilation (P= 0.039) and bronchoscopy (P= 0.026). PFGE profiles demonstrated two major clones (profiles 1 and 2) in ICU colonized and infected groups (45/52 strains tested). We calculated an attack rate infection/colonization of 28% for clone 1 and 20% for clone 2.

Seven of eight infected patients (87.5%) had the same genomic profile for colonization and infection using PFGE.

Conclusions

Our results indicate that younger age, long length of ICU stay, use of mechanical ventilation and bronchoscopy were risk factors for Ea infection in colonized patients. Ea colonization is associated with a very high risk of Ea infection by the same genomic strain. This may guide antibiotic treatment in this particular population of ICU patients.