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.
Division of Infectious Diseases, Department of Medicine, Columbia University, College of Physicians & Surgeons, New York, NY 10032, USA. eyf2002@columbia.edu
E Yoko
EY
Furuya
Heather A
HA
Cook
Mei-Ho
MH
Lee
Maureen
M
Miller
Elaine
E
Larson
Sandra
S
Hyman
Phyllis
P
Della-Latta
Eneida A
EA
Mendonca
Franklin D
FD
Lowy
D015331:Cohort Studies; D017714:Community-Acquired Infections / Q000453:epidemiology; D004812:Epidemiologic Methods; D006801:Humans; D016106:Methicillin Resistance; D009519:New York City / Q000453:epidemiology; D015995:Prevalence; D011446:Prospective Studies; D012189:Retrospective Studies; D013203:Staphylococcal Infections / Q000453:epidemiology*; D013211:Staphylococcus aureus / Q000187:drug effects*