CANWARD symposiumComparison of community-associated and health care-associated methicillin-resistant Staphylococcus aureus in Canada: results of the CANWARD 2007–2009 study
Introduction
Staphylococcus aureus infections, particularly those caused by methicillin-resistant strains, are recognized as a serious problem in both inpatient and outpatient settings and are now endemic in many regions worldwide (Naimi et al., 2003, Simor et al., 2010a). Although methicillin-resistant S. aureus (MRSA) are most often associated with health care and long-term care facilities, the emergence of community-associated MRSA (CA-MRSA) and the encroachment of these strains into the health care setting have led to a significant change in the epidemiology of MRSA throughout the past decade (Naimi et al., 2003, Nichol et al., 2009, Simor et al., 2010a, Zhanel et al., 2010).
The most common infections caused by CA-MRSA are skin and soft tissue infections, although more invasive infections involving the respiratory tract, with and without bacteremia, and septic shock can occur (Naimi et al., 2003, Otter and French, 2010, Simor et al., 2010a). Affected individuals often lack traditional risk factors for MRSA infection. Although CA-MRSA are resistant to β-lactam antibiotics, they typically remain relatively susceptible to non–β-lactam antimicrobial agents (Nichol et al., 2009, Simor et al., 2010b). Many strains produce toxins such as the Panton–Valentine leukocidin (PVL) and other virulence factors that may play a role in the increased severity of disease associated with CA-MRSA (Tristan et al., 2007). In this study, we compare the demographics, antimicrobial susceptibilities, and molecular epidemiology of community-associated and health care-associated MRSA genotypes in Canadian hospitals from 2007 to 2009, inclusive.
Section snippets
Bacterial isolates
Study isolates were obtained as part of the annual, ongoing Canadian Ward Surveillance Study (CANWARD) surveillance study from 2007 to 2009, as previously described in this symposium (Zhanel et al., 2011). Of the 18,538 isolates collected throughout the studies, 3589 were S. aureus; and of those, 889 (24.8%) were identified as MRSA (385 in 2007, 272 in 2008, and 232 in 2009). Resistance to methicillin was determined using the Clinical and Laboratory Standards Institute (CLSI, 2010) approved
Demographic comparison of CA-MRSA and HA-MRSA genotypes
From 2007 to 2009, a total of 889 MRSA (24.8% of all S. aureus) were collected. Overall, 224 (25.2%) were identified as a CA-MRSA genotype, while 644 (72.4%) were identified as an HA-MRSA genotype (Table 1). The remaining 21 (2.4%) MRSA isolates had a spa type that did not correspond with 1 of the 10 characterized Canadian epidemic types (CMRSA1–10) and were therefore deemed unique (data not shown). The prevalence of isolates with a CA-MRSA genotype increased significantly from 19.5% (75/385)
Discussion
Recently, Simor et al. (2010a) reported increasing colonization and infection due to MRSA in Canadian hospitals. Our study demonstrates the continued and rapid spread of CA-MRSA genotypes in Canadian hospitals, increasing from 19.5% of MRSA in 2007 to 31.9% in 2009 (P < .001). As previously reported, this spread is largely the result of the CMRSA10 (USA300) genotype, which contains SCCmec type IVa and is PVL-positive (Table 2) (Simor et al., 2010a). The association of CA-MRSA infections and
Acknowledgments
This paper was presented in part at the 50th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC 2010) in Boston, MA. Funding and medical center (investigator) acknowledgements are provided in the first paper of this symposium (Hoban and Zhanel, 2011).
CANWARD data can also be found at www.can-r.ca, the official website of the Canadian Antimicrobial Resistance Alliance (CARA).
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