Epidemiology of methicillin-resistant Staphylococcus aureus colonization in a surgical intensive care unit.
BACKGROUND
Methicillin-resistant Staphylococcus aureus (MRSA) is a cause of healthcare-associated infections among surgical intensive care unit (ICU) patients, though transmission dynamics are unclear.


OBJECTIVE
To determine the prevalence of MRSA nasal colonization at ICU admission, to identify associated independent risk factors, to determine the value of these factors in active surveillance, and to determine the incidence of and risk factors associated with MRSA acquisition.


METHODS
Prospective cohort study.


METHODS
Surgical ICU at a teaching hospital.


METHODS
All patients admitted to the surgical ICU.


RESULTS
Active surveillance for MRSA by nasal culture was performed at ICU admission during a 15-month period. Patients who stayed in the ICU for more than 48 hours had nasal cultures performed weekly and at discharge from the ICU, and clinical data were collected prospectively. Of 1,469 patients, 122 (8%) were colonized with MRSA at admission; 75 (61%) were identified by surveillance alone. Among 775 patients who stayed in the ICU for more than 48 hours, risk factors for MRSA colonization at admission included the following: hospital admission in the past year (1-2 admissions: adjusted odds ratio [aOR], 2.60 [95% confidence interval {CI}, 1.47-4.60]; more than 2 admissions: aOR, 3.56 [95% CI, 1.72-7.40]), a hospital stay of 5 days or more prior to ICU admission (aOR, 2.54 [95% CI, 1.49-4.32]), chronic obstructive pulmonary disease (aOR, 2.16 [95% CI, 1.17-3.96]), diabetes mellitus (aOR, 1.87 [95% CI, 1.10-3.19]), and isolation of MRSA in the past 6 months (aOR, 8.18 [95% CI, 3.38-19.79]). Sixty-nine (10%) of 670 initially MRSA-negative patients acquired MRSA in the ICU (corresponding to 10.7 cases per 1,000 ICU-days at risk). Risk factors for MRSA acquisition included tracheostomy in the ICU (aOR, 2.18 [95% CI, 1.13-4.20]); decubitus ulcer (aOR, 1.72 [95% CI, 0.97-3.06]), and receipt of enteral nutrition via nasoenteric tube (aOR, 3.73 [95% CI, 1.86-7.51]), percutaneous tube (aOR, 2.35 [95% CI, 0.74-7.49]), or both (aOR, 3.33 [95% CI, 1.13-9.77]).


CONCLUSIONS
Active surveillance detected a sizable proportion of MRSA-colonized patients not identified by clinical culture. MRSA colonization on admission was associated with recent healthcare contact and underlying disease. Acquisition was associated with potentially modifiable processes of care.
Warren
David K
DK
Division of Infectious Diseases, Washington University School of Medicine, Barnes Jewish Hospital, Saint Louis, MO 63110, USA. dwarren@im.wustl.edu
Guth
Rebecca M
RM
Coopersmith
Craig M
CM
Merz
Liana R
LR
Zack
Jeanne E
JE
Fraser
Victoria J
VJ
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D005260:Female; D013502:General Surgery; D006801:Humans; D007362:Intensive Care Units; D008297:Male; D016106:Methicillin Resistance; D008875:Middle Aged; D008962:Models, Theoretical; D009296:Nasal Cavity / Q000382:microbiology; D015995:Prevalence; D011446:Prospective Studies; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000453:epidemiology*; D013211:Staphylococcus aureus / Q000302:isolation & purification