Modeling the invasion of community-acquired methicillin-resistant Staphylococcus aureus into hospitals.
BACKGROUND
Methicillin-resistant Staphylococcus aureus (MRSA) has traditionally been associated with infections in hospitals. Recently, a new strain of MRSA has emerged and rapidly spread in the community, causing serious infections among young, healthy individuals. Preliminary reports imply that a particular clone (USA300) of a community-acquired MRSA (CA-MRSA) strain is infiltrating hospitals and replacing the traditional hospital-acquired MRSA strains. If true, this event would have serious consequences, because CA-MRSA infections in hospitals would occur among a more debilitated, older patient population.


METHODS
A deterministic mathematical model was developed to characterize the factors contributing to the replacement of hospital-acquired MRSA with CA-MRSA and to quantify the effectiveness of interventions aimed at limiting the spread of CA-MRSA in health care settings.


RESULTS
The model strongly suggests that CA-MRSA will become the dominant MRSA strain in hospitals and health care facilities. This reversal of dominant strain will occur as a result of the documented expanding community reservoir and increasing influx into the hospital of individuals who harbor CA-MRSA. Competitive exclusion of hospital-acquired MRSA by CA-MRSA will occur, with increased severity of CA-MRSA infections resulting in longer hospitalizations and a larger in-hospital reservoir of CA-MRSA.


CONCLUSIONS
Improving compliance with hand hygiene and screening for and decolonization of CA-MRSA carriers are effective strategies. However, hand hygiene has the greatest return of benefits and, if compliance is optimized, other strategies may have minimal added benefit.
D'Agata
Erica M C
EM
Division of Infectious Diseases, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02215, USA. edagata@bidmc.harvard.edu
Webb
Glenn F
GF
Horn
Mary Ann
MA
Moellering
Robert C
RC
Ruan
Shigui
S
D017714:Community-Acquired Infections / Q000453:epidemiology* / Q000382:microbiology / Q000635:transmission*; D003428:Cross Infection / Q000453:epidemiology* / Q000382:microbiology*; D006235:Hand Disinfection; D006801:Humans; D017053:Infection Control / Q000379:methods; D055624:Methicillin-Resistant Staphylococcus aureus / Q000302:isolation & purification*; D008962:Models, Theoretical; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology / Q000635:transmission*