Main Menu Browse by Day or Program Author Keywords

250 Linking molecular subtyping with clinical characteristics of patients with USA 300 methicillin resistant Staphylococcus aureus infections

Saturday, April 2, 2011
Trinity Ballroom (Hilton Anatole)
Legesse Mekonnen, MD , The Ohio State University Medical Center, Columbus, OH
Richard Bakker, MD, PhD , The Ohio State University Medical Center, Columbus, OH
Shu-Hua Wang, MD, MPH&TM , The Ohio State University Medical Center, Columbus, OH
Yosef Khan, MBBS, MPH , The Ohio State University Medical Center, Columbus, OH
Lisa Hines, RN, CIC , The Ohio State University Medical Center, Columbus, OH
Kurt Stevenson, MD, MPH , The Ohio State University Medical Center, Columbus, OH
Background:

MRSA is an increasingly important cause of severe infections. These infections are categorized epidemiologically as hospital acquired (HA), healthcare-associated with community onset (HACO) or community onset (CO). Molecular typing is crucial in evaluating local outbreaks and wide-scale dissemination of specific clones.  As part of a large MRSA surveillance program in the state of Ohio, we linked the clinical characteristics and risk factors of USA 300 MRSA cases with additional molecular characterization

Objective:

Link clinical characteristics with molecular subtyping of USA 300 MRSA isolates to identify the major responsible strains and associated risk factors

Methods:

Molecular subtyping of USA 300 MRSA isolates using repetitive element Polymerase Chain Reaction (rep-PCR: DiversiLabTM, Biomerieux, NC), Staphylococcus chromosome cassette (SCC) mecA typing methods, and medical record review of 503 patients seen at a tertiary medical center and 7 referring community hospitals from 01/07/2007 to 06/30/2010. Rep-PCR strains were assigned arbitrary numeric classifications

Results:

Among patients with USA 300 infections, 503 subjects (266 male, 237 female) aged 18-93 years were evaluated (391white, 96 blacks).  Bacteremia occurred in 94 (18.4%). There were 367 (73.3%) CO, 50 (9.8%) HA, and 86(17%) HACO. Patient outcomes included 18 (4.2%) deaths, 26 (5.73%) relapses, 91 (20%) cure, 7 (1.54%) treatment failure, and 312 (68.5%) unknown outcome. Mortality in non-bacteremic patients was 2.5% compared to 10.6 % in bacteremic patients. SCCmecA type IVa accounted 333 (67.5%) of the 493 isolates and 160 (32.5%) were type IVb. There were 15 different strains isolated by Rep-PCR genotyping. Rep-PCR strain 9 and 63 accounted for 233 (40.5%) and 154 (26.6%) infections, respectively. No single Rep-PCR strain is dominant in either CA or HA/HACO infections.  Most isolates (n=280, 80.7%) had vancomycin MIC ≤2. At least one HA-MRSA risk factor is present in 16 (88.9 %) of those who died and in 40 (78.4 %) of those with poor outcome (death, treatment failure or relapse). Sixteen of the 18 deaths were HA or HACO infections. Poor patient outcomes were marginal association with rep-PCR strains 13 and 52 (p-value, 0.07). Rep-PCR strain 52 is weakly associated with past history of MRSA infection (p-value, 0.06), and strain 63 is also marginally associated with long-term facility residency (p-value, 0.09). The majority of patients with poor outcomes had Vancomycin MIC≥2 (p-value 0.1)

Conclusions:

Rep-PCR subtype 9 and 63 are responsible for the majority of USA 300 MRSA infections in our study population. Consistent with previous studies, the majority of infections caused by USA 300 MRSA in our data set are community associated. There does not appear to be significant association between rep-PCR strain types and poor outcomes