Molecular and phenotypic characteristics of healthcare- and community-associated methicillin-resistant Staphylococcus aureus at a rural hospital.
BACKGROUND
While methicillin-resistant Staphylococcus aureus (MRSA) originally was associated with healthcare, distinct strains later emerged in patients with no prior hospital contact. The epidemiology of MRSA continues to evolve.


METHODS
To characterize the current epidemiology of MRSA-colonized patients entering a hospital serving both rural and urban communities, we interviewed patients with MRSA-positive admission nasal swabs between August 2009 and March 2010. We applied hospitalization risk factor, antimicrobial resistance phenotype, and multi-locus sequence genotype (MLST) classification schemes to 94 case-patients.


RESULTS
By MLST analysis, we identified 15 strains with two dominant clonal complexes (CCs)-CC5 (51 isolates), historically associated with hospitals, and CC8 (27 isolates), historically of community origin. Among patients with CC5 isolates, 43% reported no history of hospitalization within the past six months; for CC8, 67% reported the same. Classification by hospitalization risk factor did not correlate strongly with genotypic classification. Sensitivity of isolates to ciprofloxacin, clindamycin, or amikacin was associated with the CC8 genotype; however, among CC8 strains, 59% were resistant to ciprofloxacin, 15% to clindamycin, and 15% to amikacin.


CONCLUSIONS
Hospitalization history was not a strong surrogate for the CC5 genotype. Conversely, patients with a history of hospitalization were identified with the CC8 genotype. Although ciprofloxacin, clindamycin, and amikacin susceptibility distinguished CC8 strains, the high prevalence of ciprofloxacin resistance limited its predictive value. As CC8 strains become established in healthcare settings and CC5 strains disseminate into the community, community-associated MRSA definitions based on case-patient hospitalization history may prove less valuable in tracking community MRSA strains.
Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States of America.
Amy E
AE
Peterson
Meghan F
MF
Davis
Kathleen G
KG
Julian
Grace
G
Awantang
Wallace H
WH
Greene
Lance B
LB
Price
Andrew
A
Waters
Avanthi
A
Doppalapudi
Lisa J
LJ
Krain
Kenrad
K
Nelson
Ellen K
EK
Silbergeld
Cynthia J
CJ
Whitener
D017714:Community-Acquired Infections / Q000382:microbiology*; D003428:Cross Infection / Q000382:microbiology*; D006780:Hospitals, Rural; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000235:genetics / Q000472:pathogenicity*; D008826:Microbial Sensitivity Tests; D010641:Phenotype; D013203:Staphylococcal Infections / Q000382:microbiology*