Community-associated methicillin-resistant Staphylococcus aureus prevalence: How common is it? A methodological comparison of prevalence ascertainment
Background
Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are becoming increasingly prevalent. There is geographic variation in their reported prevalence across the United States; however, studies reporting on CA-MRSA prevalence also demonstrate great variability in their case-finding methodology. We conducted a study to see how three different methods to ascertain CA-MRSA prevalence would lead to different estimates.
Methods
Different methods were used to identify cases of CA-MRSA colonization and/or infection in New York City. Method 1: retrospective review of clinical and surveillance cultures identified through a hospital computer database. Method 2: prospective collection of surveillance cultures in the same hospital's emergency department. Method 3: prospective collection of surveillance cultures in a community setting.
Results
Differing values for CA-MRSA prevalence resulted depending on the method and denominator used. All nares cultures as the denominator led to prevalence estimates of 0.3%-0.6%; all S. aureus as the denominator led to rates of 1.2%-5%; all MRSA as the denominator led to estimates of 5.5%-50%.
Conclusions
A comparison of three methods revealed that variability in case-finding methodologies can lead to different prevalence estimates. Key factors to consider when comparing CA-MRSA rates include the definition of CA-MRSA, choice of denominator, and method and setting of sample collection.
New York, New York
aFrom the Division of Infectious Diseases, Department of Medicine, Columbia University, College of Physicians & Surgeons, New York, NY
bColumbia University, Mailman School of Public Health, New York, NY
cColumbia University, School of Nursing and Mailman School of Public Health, New York, NY
dDepartment of Epidemiology, NewYork-Presbyterian Hospital, New York, NY
eDepartment of Pathology, Columbia University, College of Physicians & Surgeons, New York, NY
fDepartment of Biomedical Informatics, Columbia University, College of Physicians and Surgeons, New York, NY
Address correspondence to E. Yoko Furuya, MD, 630 W. 168th St., PH-8W #876, New York, NY 10032.
Supported by the National Institutes of Health grants K23 AI01752-01A1 and R01 AI60859-01A1.
ABSTRACT