Fifteen-year study of the changing epidemiology of methicillin-resistant Staphylococcus aureus.
OBJECTIVE
The study's purpose was to elucidate the evolutionary, microbiologic, and clinical characteristics of methicillin-resistant Staphylococcus aureus (MRSA) infections.


METHODS
MRSA cases from military medical facilities in San Diego, from 1990 to 2004, were evaluated and categorized as community-acquired or nosocomial. Sequence type, staphylococcal chromosomal cassette gene type, and Panton-Valentine leukocidin gene status were determined for a subset of isolates.


RESULTS
Over the 15-year period, 1888 cases of MRSA were identified; 65% were community acquired. The incidence (155 infections/100000 person-year in 2004) and household-associated cases rapidly increased since 2002. Among persons with community-acquired MRSA, 16% were hospitalized and only 17% were initially given an effective antibiotic. Community-acquired MRSA cases compared with nosocomial MRSA cases were more often soft-tissue and less often urinary, lung, or bloodstream infections (P<.001). Patients with community-acquired MRSA were younger (22 vs 64 years, P<.001) and less likely to have concurrent medical conditions (9% vs 98%, P<.001). Clindamycin resistance increased among community-acquired MRSA isolates during 2003 and 2004 compared with previous years (79% vs 13%, P<.001). Genetically, nosocomial MRSA isolates were significantly different than those acquired in the community. Although community-acquired MRSA isolates were initially diverse by 2004, one strain (staphylococcal chromosomal cassette type IV, sequence type 8, Panton-Valentine leukocidin gene positive) became the predominant isolate.


CONCLUSIONS
Community-acquired and intrafamilial MRSA infections have increased rapidly since 2002. Our 15 years of surveillance revealed the emergence of distinct community-acquired MRSA strains that were genetically unrelated to nosocomial MRSA isolates from the same community.
Crum
Nancy F
NF
Infectious Diseases Division, Naval Medical Center San Diego, San Diego, Calif 92134-1005, USA. NFCrum@nmcsd.med.navy.mil
Lee
Rachel U
RU
Thornton
Scott A
SA
Stine
O Colin
OC
Wallace
Mark R
MR
Barrozo
Chris
C
Keefer-Norris
Ananda
A
Judd
Sharon
S
Russell
Kevin L
KL
D000328:Adult; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D002140:California / Q000453:epidemiology; D002981:Clindamycin / Q000627:therapeutic use; D017714:Community-Acquired Infections / Q000453:epidemiology / Q000382:microbiology; D003428:Cross Infection / Q000188:drug therapy / Q000453:epidemiology* / Q000382:microbiology*; D024881:Drug Resistance, Bacterial; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D016106:Methicillin Resistance; D013203:Staphylococcal Infections / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics
D000900:Anti-Bacterial Agents; D002981:Clindamycin