Epidemiology of healthcare-associated bloodstream infection caused by USA300 strains of methicillin-resistant Staphylococcus aureus in 3 affiliated hospitals.
OBJECTIVE
To describe the epidemiology of bloodstream infection caused by USA300 strains of methicillin-resistant Staphylococcus aureus (MRSA), which are traditionally associated with cases of community-acquired infection, in the healthcare setting.


METHODS
Retrospective cohort study.


METHODS
Three academically affiliated hospitals in Denver, Colorado.


METHODS
Review of cases of S. aureus bloodstream infection during the period from 2003 through 2007. Polymerase chain reaction was used to identify MRSA USA300 isolates.


RESULTS
A total of 330 cases of MRSA bloodstream infection occurred during the study period, of which 286 (87%) were healthcare-associated. The rates of methicillin resistance among the S. aureus isolates recovered did not vary during the study period and were similar among the 3 hospitals. However, the percentages of cases of healthcare-associated MRSA bloodstream infection due to USA300 strains varied substantially among the 3 hospitals: 62%, 19%, and 36% (P<.001) for community-onset cases and 33%, 3%, and 33% (P=.005) for hospital-onset cases, in hospitals A, B, and C, respectively. In addition, the number of cases of healthcare-associated MRSA bloodstream infection caused by USA300 strains increased during the study period at 2 of the 3 hospitals. At each hospital, USA300 strains were most common among cases of community-associated infection and were least common among cases of hospital-onset infection. Admission to hospital A (a safety-net hospital), injection drug use, and human immunodeficiency virus infection were independent risk factors for healthcare-associated MRSA bloodstream infection due to USA300 strains.


CONCLUSIONS
The prevalence of USA300 strains among cases of healthcare-associated MRSA bloodstream infection varied dramatically among geographically clustered hospitals. USA300 strains are replacing traditional healthcare-related strains of MRSA in some healthcare settings. Our data suggest that the prevalence of USA300 strains in the community is the dominant factor affecting the prevalence of this strain type in the healthcare setting.
Jenkins
Timothy C
TC
Division of Infectious Diseases, Denver Health, CO 80204, USA. timothy.jenkins@dhha.org
McCollister
Bruce D
BD
Sharma
Rohini
R
McFann
Kim K
KK
Madinger
Nancy E
NE
Barron
Michelle
M
Bessesen
Mary
M
Price
Connie S
CS
Burman
William J
WJ
D016470:Bacteremia / Q000453:epidemiology* / Q000382:microbiology; D015331:Cohort Studies; D017714:Community-Acquired Infections / Q000453:epidemiology / Q000235:genetics / Q000382:microbiology; D003428:Cross Infection / Q000453:epidemiology* / Q000382:microbiology; D004269:DNA, Bacterial / Q000235:genetics; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000235:genetics / Q000302:isolation & purification*; D017720:Molecular Epidemiology; D012189:Retrospective Studies; D012307:Risk Factors; D013203:Staphylococcal Infections / Q000097:blood / Q000453:epidemiology* / Q000382:microbiology
D004269:DNA, Bacterial