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


METHODS
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.


METHODS
An urban hospital in San Francisco, California.


METHODS
During the outbreak period, December 1997 through January 1998, there were 52 patients with a minimum ICU stay of > or = 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.
Dorsey
G
G
Epidemiology and Prevention Interventions Center at San Francisco General Hospital, University of California-San Francisco, 94110, USA.
Borneo
H T
HT
Sun
S J
SJ
Wells
J
J
Steele
L
L
Howland
K
K
Perdreau-Remington
F
F
Bangsberg
D R
DR
D015331:Cohort Studies; D003428:Cross Infection; D004269:DNA, Bacterial / Q000032:analysis; D004196:Disease Outbreaks; D016521:Electrophoresis, Gel, Pulsed-Field; D016972:Enterobacter cloacae / Q000235:genetics / Q000302:isolation & purification / Q000472:pathogenicity*; D004756:Enterobacteriaceae Infections / Q000453:epidemiology*; D006786:Hospitals, Urban; D006801:Humans; D017053:Infection Control; D007362:Intensive Care Units; D017720:Molecular Epidemiology; D009741:Nursing Staff, Hospital / Q000600:supply & distribution; D012189:Retrospective Studies; D012307:Risk Factors; D016868:Serratia Infections / Q000453:epidemiology*; D012706:Serratia marcescens / Q000235:genetics / Q000302:isolation & purification / Q000472:pathogenicity*
D004269:DNA, Bacterial