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690 Understanding inter-facility transmission of Methicillin Resistant Staphylococcus aureus (MRSA): The role of traditional and molecular epidemiologic methods

Saturday, March 20, 2010: 3:00 PM
Regency VI-VII (Hyatt Regency Atlanta)
Shu-Hua Wang, MD, MPH , The Ohio State University Medical Center, Columbus, OH
Yosef Khan, MBBS, MPH , The Ohio State University Medical Center, Columbus, OH
Rachel L. DeMita, M.D. , The Ohio State University Medical Center, Columbus, OH
Lisa Hines, RN, CIC , The Ohio State University Medical Center, Columbus, OH
Ruchi Soni, BS , The Ohio State University Medical Center, Columbus, OH
Preeti Pancholi, PhD , The Ohio State University Medical Center, Columbus, OH
Kurt B. Stevenson, MD, MPH , The Ohio State University Medical Center, Columbus, OH
Background: MRSA is an increasing cause of healthcare-associated (HA) and community -associated (CA) infections. Historically, HA-MRSA and CA-MRSA differed in specific MRSA strains types and antibiotic resistance patterns.  CA-MRSA strains often occur in younger patients, tend to be less resistant to non-β-lactam antibiotics, and are more often associated with skin and soft tissue infections (SSTI). However, recent studies have shown that CA-MRSA strains are now causing infections in healthcare settings.
Objective: To compare clinical characteristics and molecular genotypes of MRSA isolates from a tertiary medical center (MC) and 7 referring community hospitals (CH) to help understand if transmission of CA- and HA-MRSA is occurring between these facilities.   
Methods: Molecular genotyping and medical chart reviews were conducted on 337 patients with MRSA clinical infections from January 2007 to July 2009:  152 retrospective archived MRSA isolates from MC for baseline prevalence; 116 consecutive prospective isolates from CH; and 69 randomized prospective isolates from MC.  Molecular genotyping was performed by repetitive element Polymerase Chain Reaction (rep-PCR; DiversiLab,TM Biomerieux, NC). Pulse Field Gel Electrophoresis (PFGE) and Staphylococcal chromosome cassette (SCC) mecA typing were derived from DiversiLab MRSA library.  PFGE was confirmed on 24 selected representative repPCR isolate patterns.
Results: The isolates were distributed into 41 different rep-PCR genotype patterns. 271/337 (80%) of the isolates were clustered into 6 major patterns (A to F; 14-130 isolates).  Clinical and molecular characteristics along with antibiotic susceptibilities (SUSCEPT) for clinidamycin (CLIN), tetracycline (TCN), and Trimethoprim-sulfamethoxizole (TMP/SXT) of the six major patterns are listed below.   

RepPCR Type

A
B
C
D
E
F
Total number (n)
14
61
24
130
18
24
PFGE USA type
100
100
Brazilian
300
300
100
SCC mecA type
II
II
III
IVa
IVa
II
Gender % male
64
35
57
57
43
38
Median Age
70
61
57
45
37
66
White Race (%)
64
90
87
76
86
86
% CH
14
20
13
45
56
33
%MC
86
80
87
55
44
67
Blood (%)
14
28
42
19
6
50
SSTI (%)
14
23
8
53
78
17
CLIN SUSCEPT (%)
0
5
0
66
88
7
TCN SUSCEPT (%)
100
94
10
98
100
85
TMP/SXT SUSCEPT (%)
100
98
36
97
100
100
CA-MRSA (%)
21
12
9
59
92
15
HA-MRSA (%)
79
88
91
41
8
85

Conclusions: Distinct molecular and epidemiological characteristics exist between MRSA isolates within this referral network of hospitals.  CA- and HA-MRSA strains were commonly shared in both the MC and CH, but relative proportions were different.  We predict the applications of these tools combined with continued surveillance, social network and temporospatial analysis will allow a more complete understanding of MRSA transmission between facilities.