Molecular epidemiology of methicillin-resistant Staphylococcus aureus in a Veterans Administration Medical Center.
OBJECTIVE
To determine whether patients who were colonized or infected with methicillin-resistant Staphylococcus aureus (MRSA) persistently carried the same strain and to identify the extent of strain variation within a population of patients.


METHODS
Molecular typing by pulsed-field gel electrophoresis (PFGE) of stored MRSA isolates.


METHODS
A Veterans Administration Medical Center with 288 hospital, 45 intermediate-care, and 75 extended-care beds. ISOILATES: Between January 1991 and March 1993, 91 patients had MRSA identified in routine cultures. One hundred isolates from 57 patients (63%) were available for typing.


RESULTS
Before 1988, only occasional MRSA isolates were identified. By 1993, 50% of S. aureus isolates from unique patients were resistant to methicillin. PFGE identified 7 MRSA strains, 3 of which were identified in specimens from 1 patient each. The most common strains were SD4 (20 patients), SD1 (12 patients), SD2 (12 patients), and SD5a (5 patients). Twenty patients had 2 or more isolates obtained at least 1 week apart (mean, 30.7 weeks; range, 1 to 102 weeks). Of these patients, 12 were colonized or infected with only one strain (mean time observed, 25.1 weeks; range, 1 to 82 weeks). Eight patients had at least 2 different strains (mean time observed, 39 weeks; range, 2 to 102 weeks).


CONCLUSIONS
Numerous MRSA strains circulated in this endemic setting, 40% of patients observed over time were colonized or infected with more than one strain. Molecular typing was an essential tool for evaluating the epidemiology of MRSA in this setting.
Herwaldt
Loreen A
LA
The University of Iowa Hospitals and Clinics, Iowa City 52242-081, USA.
Pottinger
Jean M
JM
Coffman
Stacy
S
Tjaden
Jean
J
D015373:Bacterial Typing Techniques; D003428:Cross Infection / Q000453:epidemiology* / Q000382:microbiology*; D004269:DNA, Bacterial / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D019353:Endemic Diseases / Q000706:statistics & numerical data; D005500:Follow-Up Studies; D006787:Hospitals, Veterans; D006801:Humans; D017053:Infection Control; D016106:Methicillin Resistance / Q000235:genetics*; D017720:Molecular Epidemiology; D011159:Population Surveillance; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000235:genetics*; D014481:United States / Q000453:epidemiology; D014493:United States Department of Veterans Affairs
D004269:DNA, Bacterial