Original Article

Dissemination of Community-Associated Methicillin-Resistant Staphylococcus aureus in a Tertiary Care Hospital

Authors: Mukesh Patel, MD, Craig J. Hoesley, MD, Stephen A. Moser, PhD, Alan M. Stamm, MD, John W. Baddley, MD, Ken B. Waites, MD

Abstract

Background: The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) was investigated at a tertiary care hospital, and relationship was made between the clinical and genetic definitions of community- and healthcare-associated MRSA.


Methods: Nonduplicate isolates of S aureus were collected during 2004. Isolates were classified clinically as community-associated (CA) or healthcare-associated (HA). Molecular typing studies were performed on the isolates.


Results: Four hundred and two S aureus isolates were collected, of which 281 (70%) were MRSA. By clinical definition, 58 (21%) were classified as CA-MRSA and 215 (77%) as HA-MRSA. Among CA-MRSA, 36 (62%) harbored a SCCmec type IV gene. None of the SCCmec type IV CA-MRSA expressed inducible clindamycin resistance (MLSBi). Among 57 HA-MRSA isolates, 31 (54.4%) harbored a SCCmec type IV gene; MLSBi present in 5 (16%). Type IV SCCmec MRSA were most often associated with skin and soft tissue infections (RR 3.34 95% CI 1.43, 7.8). USA300 was the most common genotype among both CA- and HA-MRSA.


Conclusions: Community-associated MRSA is a prominent pathogen with its most common genotype, USA300, representing a significant proportion of CA- and HA-MRSA infections in our institution. Clinical definitions of CA- and HA- status do not correlate well with the genetic definitions, particularly for HA-MRSA.


Key Points


* Clinical and genetic definitions for community-associated and healthcare associated methicillin-resistant Staphylococcus aureus do not correlate well.


* Community-associated methicillin-resistant Staphylococcus aureus has become a prominent cause of infections in patients with traditional risk-factors for healthcare-associated MRSA infection.


* The USA300 genotype of CA-MRSA is the most common genotype of MRSA isolated among clinically designated community and healthcare associated MRSA at our institution.


* Inducible clindamycin resistance remains uncommon among CA-MRSA strains.

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