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Methicillin-Resistant Staphylococcus aureus (MRSA) Nasal Carriage in Residents of Veterans Affairs Long-Term Care Facilities: Role of Antimicrobial Exposure and MRSA Acquisition

  • Nimalie D. Stone (a1), Donna R. Lewis (a2), Theodore M. Johnson (a1) (a2), Thomas Hartney (a3), Doris Chandler (a4), Johnita Byrd-Sellers (a2), John E. McGowan (a5), Fred C. Tenover (a6), John A. Jernigan (a6) and Robert P. Gaynes (a2)...

Abstract

Objective.

To identify risk factors associated with methicillin-resistant Staphylococcus aureus (MRSA) acquisition in long-term care facility (LTCF) residents.

Design.

Multicenter, prospective cohort followed over 6 months.

Setting.

Three Veterans Affairs (VA) LTCFs.

Participants.

All current and new residents except those with short stay (<2 weeks).

Methods.

MRSA carriage was assessed by serial nares cultures and classified into 3 groups: persistent (all cultures positive), intermittent (at least 1 but not all cultures positive), and noncarrier (no cultures positive). MRSA acquisition was defined by an initial negative culture followed by more than 2 positive cultures with no subsequent negative cultures. Epidemiologic data were collected to identify risk factors, and MRSA isolates were typed by pulsed-field gel electrophoresis (PFGE).

Results.

Among 412 residents at 3 LTCFs, overall MRSA prevalence was 58%, with similar distributions of carriage at all 3 facilities: 20% persistent, 39% intermittent, 41% noncarriers. Of 254 residents with an initial negative swab, 25 (10%) acquired MRSA over the 6 months; rates were similar at all 3 LTCFs, with no clusters evident. Multivariable analysis demonstrated that receipt of systemic antimicrobials during the study was the only significant risk factor for MRSA acquisition (odds ratio, 7.8 [95% confidence interval, 2.1–28.6]; P = .002). MRSA strains from acquisitions were related by PFGE to those from a roommate in 9/25 (36%) cases; 6 of these 9 roommate sources were persistent carriers.

Conclusions.

MRSA colonization prevalence was high at 3 separate VA LTCFs. MRSA acquisition was strongly associated with antimicrobial exposure. Roommate sources were often persistent carriers, but transmission from roommates accounted for only approximately one-third of MRSA acquisitions.

Copyright

Corresponding author

Division of Healthcare Quality Promotion, Centers for Disease Control and Prevention, 1600 Clifton Road, Building 16, MS:A-31, Atlanta, GA 30333 (nstone@cdc.gov)

References

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Infection Control & Hospital Epidemiology
  • ISSN: 0899-823X
  • EISSN: 1559-6834
  • URL: /core/journals/infection-control-and-hospital-epidemiology
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