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A Heterogeneous Outbreak of Enterobacter cloacae and Serratia marcescens Infections in a Surgical Intensive Care Unit

Published online by Cambridge University Press:  02 January 2015

Grant Dorsey
Affiliation:
Epidemiology and Prevention Interventions Center at San Francisco General Hospital, University of California–San Francisco
Hena T. Borneo
Affiliation:
Epidemiology and Prevention Interventions Center at San Francisco General Hospital, University of California–San Francisco
Sumi J. Sun
Affiliation:
Epidemiology and Prevention Interventions Center at San Francisco General Hospital, University of California–San Francisco
Jennifer Wells
Affiliation:
Epidemiology and Prevention Interventions Center at San Francisco General Hospital, University of California–San Francisco
Lynn Steele
Affiliation:
Epidemiology and Prevention Interventions Center at San Francisco General Hospital, University of California–San Francisco
Kathryn Howland
Affiliation:
Epidemiology and Prevention Interventions Center at San Francisco General Hospital, University of California–San Francisco
Francoise Perdreau-Remington
Affiliation:
Epidemiology and Prevention Interventions Center at San Francisco General Hospital, University of California–San Francisco
David R. Bangsberg*
Affiliation:
Epidemiology and Prevention Interventions Center at San Francisco General Hospital, University of California–San Francisco
*
Epidemiology and Prevention Interventions Center at San Francisco General Hospital, University of California–San Francisco, 1001 Potrero Ave, Building 100, Room 301, San Francisco, CA 94110, db@epi-center.ucsf.edu

Abstract

Objective:

To investigate an outbreak of invasive disease due to Enterobacter cloacae and Serratia marcescens in a surgical intensive care unit (ICU).

Design:

Pulsed-field gel electrophoresis (PFGE) analysis of restriction fragments was used to characterize the outbreak isolate genotypes. A retrospective cohort study of surgical ICU patients was conducted to identify risk factors associated with invasive disease. Unit staffing data were analyzed to compare staffing levels during the outbreak to those prior to and following the outbreak.

Setting:

An urban hospital in San Francisco, California.

Patients:

During the outbreak period, December 1997 through January 1998, there were 52 patients with a minimum ICU stay of ≥72 hours. Of these, 10 patients fit our case definition of recovery of E cloacae or S marcescens from a sterile site.

Results:

PFGE analysis revealed a highly heterogeneous population of isolates. Bivariate analysis of patient-related risk factors revealed duration of central lines, respiratory colonization, being a burn patient, and the use of gentamicin or nafcillin to be significantly associated with invasive disease. Both respiratory colonization and duration of central lines remained statistically significant in a multivariate analysis. Staffing data suggested a temporal correlation between understaffing and the outbreak period.

Conclusions:

Molecular epidemiological techniques provided a rapid means of ruling out a point source or significant cross-contamination as modes of transmission. In this setting, patient-related risk factors, such as respiratory colonization and duration of central lines, may provide a focus for heightened surveillance, infection control measures, and empirical therapy during outbreaks caused by common nosocomial pathogens. In addition, understaffing of nurses may have played a role in this outbreak, highlighting the importance of monitoring staffing levels.

Type
Original Articles
Copyright
Copyright © The Society for Healthcare Epidemiology of America 2000

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