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295 Differences in MRSA Strains from Pediatric and Adult Hospital Patients in Orange County (OC), CA

Saturday, April 2, 2011: 2:15 PM
Coronado A (Hilton Anatole)
Lyndsey O. Hudson, MSc , Division of Infectious Disease Epidemiology, Imperial College London, London, England
Brian Spratt, PhD , Division of Infectious Disease Epidemiology, Imperial College London, London, England
Courtney Reynolds, MS , School of Social Ecology and Division of Infectious Diseases, University of California Irvine School of Medicine, Irvine, CA
Leah Terpstra, BA , Division of Infectious Diseases and Health Policy Research Institute, University of California, Irvine School of Medicine, Irvine, CA
Adrijana Gombosev, BS , Division of Infectious Diseases and Health Policy Research Institute, University of California, Irvine School of Medicine, Irvine, CA
Paul Hannah, BS , Orange County Public Healthcare Agency, Santa Ana, CA
Lydia Mikhail, MBA , Orange County Public Healthcare Agency, Santa Ana, CA
Richard Alexander, MPH , Division of Infectious Disease Epidemiology, Imperial College London, London, England
Douglas Moore, PhD , Division of Infectious Disease Epidemiology, Imperial College London, London, England
Susan S. Huang, MD, MPH , Division of Infectious Diseases and Health Policy Research Institute, University of California, Irvine School of Medicine, Irvine, CA

 

Background: The US epidemics of community and healthcare associated MRSA have suggested differences in MRSA strains in adults and children.

Comprehensive population based studies exploring these differences are lacking.

Objective: Characterize differences in pediatric (<18yo) vs. adult MRSA strains, from a population based sample.

Methods: We conducted a prospective cohort study of inpatients in OC, CA, collecting all clinical MRSA isolates (first per patient) from 97% (30/31) of the county's hospitals.  Adult isolates were collected over a 5 month period and pediatric isolates over a 12 month period in 2009. Patient data included age in years, specimen source, specimen location (ICU/non-ICU) and onset (hospital ≥3 days; community <3 days). Hospital characteristics included annual admissions, % Medicaid insured patients and % Hispanic patients. All isolates were characterized by spa typing. Data elements were tested for association with spa type t008 (USA300) in bivariate and multivariate models, clustered by hospital. Annual adult and pediatric population estimates of MRSA clinical cultures were calculated by spa type, accounting for duration of collection.

Results: We collected 1,124 adult and 159 pediatric MRSA isolates. Three spa types dominated in the county (Figure), with t008, t242, and t002 composing 83% of all isolates. The distribution among adults (t008 (41%), t242 (23%), t002 (19%)) was significantly different than among children (t008 (67%), t242 (9%), t002 (8%)), (χ²=44.3, p<0.001). In bivariate tests of individual characteristics, the % t008 was significantly higher among pediatric patients (67% vs. 41%, p<0.001), wound specimens (59% vs. 33%, p<0.001), non-ICU wards (47% vs. 28%, p<0.001), and community onset MRSA (48% vs. 37%, p=0.001). Among hospital characteristics, % Medicaid insured patients was linearly associated with t008. In multivariate testing, pediatric patients (OR=1.7 (1.0, 2.8), p=0.044), wound specimens (OR=2.4 (1.9, 3.0), p<0.001), non-ICU wards (OR=1.7 (1.2, 2.4), p=0.005), community-onset MRSA (OR=1.3 (1.0, 1.7), p=0.036), and admission to a hospital with a high % of Medicaid-insured patients (OR=1.2 (1.1, 1.4) per 10% increase in % Medicaid insured, p<0.001) significantly predicted isolation of t008. OC population estimates of clinical MRSA isolates were 122/100,000 adults and 21/100,000 children. This included 50/100,000 adults and 14/100,000 children for t008, 28/100,000 adults and 2/100,000 children for t242, and 23/100,000 adults and 1/100,000 children for t002.

Conclusions: In a large county, pediatric MRSA isolates were more likely to be spa type t008 (USA300) and associated with wounds, non ICU care, community onset, and admission to a hospital with a high % of Medicaid insured patients. While community and hospital associated MRSA reservoirs have begun to merge, significant differences remain in pediatric vs. adult patient populations.