A population-based study of the incidence and molecular epidemiology of methicillin-resistant Staphylococcus aureus disease in San Francisco, 2004-2005.
BACKGROUND
Methicillin-resistant Staphylococcus aureus (MRSA) infections have become a major public health problem in both the community and hospitals. Few studies have characterized the incidence and clonal composition of disease-causing strains in an entire population. Our objective was to perform a population-based survey of the clinical and molecular epidemiology of MRSA disease in San Francisco, California.


METHODS
We prospectively collected 3985 MRSA isolates and associated clinical and demographic information over a 12-month period (2004-2005) at 9 San Francisco-area medical centers. A random sample of 801 isolates was selected for molecular analysis.


RESULTS
The annual incidence of community-onset MRSA disease among San Francisco residents was 316 cases per 100,000 population, compared with 31 cases per 100,000 population for hospital-onset disease. Persons who were aged 35-44 years, were men, and were black had the highest incidence of community-onset disease. The USA300 MRSA clone accounted for 234 cases of community-onset disease and 15 cases of hospital-onset disease per 100,000 population, constituting an estimated 78.5% and 43.4% of all cases of MRSA disease, respectively. Patients with community-onset USA300 MRSA versus non-USA300 MRSA disease were more likely to be male, be of younger age, and have skin and soft-tissue infections. USA300 strains were generally more susceptible to multiple antibiotics, although decreased susceptibility to tetracycline was observed in both community-onset (P = .008) and hospital-onset (P = .03) USA300 compared to non-USA300 strains.


CONCLUSIONS
The annual incidence of community-onset MRSA disease in San Francisco is substantial, surpassing that of hospital-onset disease. USA300 is the predominant clone in both the community and hospitals. The dissemination of USA300 from the community into the hospital setting has blurred its distinction as a community-associated pathogen.
Liu
Catherine
C
Div. of Infectious Diseases, University of California, San Francisco, 513 Parnassus Ave., S-380, Box 0654, San Francisco, CA 94143, USA. catherine.liu@ucsf.edu
Graber
Christopher J
CJ
Karr
Michael
M
Diep
Binh An
BA
Basuino
Li
L
Schwartz
Brian S
BS
Enright
Mark C
MC
O'Hanlon
Simon J
SJ
Thomas
Jonathon C
JC
Perdreau-Remington
Francoise
F
Gordon
Shelley
S
Gunthorpe
Helen
H
Jacobs
Richard
R
Jensen
Peter
P
Leoung
Gifford
G
Rumack
James S
JS
Chambers
Henry F
HF
D000328:Adult; D017714:Community-Acquired Infections / Q000453:epidemiology* / Q000382:microbiology; D005260:Female; D006801:Humans; D008297:Male; D016106:Methicillin Resistance; D017720:Molecular Epidemiology; D011159:Population Surveillance; D011446:Prospective Studies; D012495:San Francisco / Q000453:epidemiology; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology* / Q000635:transmission; D013207:Staphylococcal Skin Infections / Q000453:epidemiology / Q000382:microbiology / Q000503:physiopathology; D013211:Staphylococcus aureus