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CA-MRSA: Now in the Hospital
One CA-MRSA genotype accounted for 8% of the nosocomial MRSA bacteremias in an Atlanta hospital.
Methicillin-resistant Staphylococcus aureus (MRSA), endemic in most U.S. hospitals and long-term–care facilities, has recently emerged as an important cause of community-acquired (CA) infection. However, CA-MRSA strains differ from healthcare-associated strains in having a smaller version of the chromosomal cassette mec element (SCCmecIV) and in usually containing genes encoding for Panton-Valentine leukocidin, a leukocyte-killing exotoxin. Furthermore, they are generally associated with skin and soft-tissue infections, not bacteremia. Of the eight genetic clusters of MRSA identified in the U.S., CA-MRSA belongs to two: USA300 and USA400. Researchers recently undertook a prospective study at a large Atlanta hospital to determine whether USA300 strains have become a common cause of bacteremia in healthcare settings.
Over 7.5 months, 132 cases of MRSA bacteremia occurred. Thirty-nine (34%) of the 116 isolates available for analysis were of the CA-MRSA USA300 genotype. In 10 of these 39 instances (8% of all cases), the bacteremia was nosocomially acquired. Factors significantly associated with isolation of the USA300 genotype were concurrent skin or soft-tissue infection (odds ratio, 3.67; 95% confidence interval, 1.10–12.28) and injection-drug use (OR, 4.26; 95% CI, 1.08–16.84).
Comment: Despite a somewhat confusing categorization of cases and presentation of numbers, the study findings demonstrate that CA-MRSA strains are creeping into the hospital environment and can cause bacteremia, albeit in the setting of soft-tissue infections. As the authors mention, no simple way exists to prevent the spread of this organism. Moreover, most clinical laboratories lack the technical ability to distinguish CA-MRSA from other MRSA genotypes.
— Neil M. Ampel, MD
Published in Journal Watch Infectious Diseases March 24, 2006
Citation(s):
Seybold U et al. Emergence of community-associated methicillin-resistant Staphylococcus aureus USA300 genotype as a major cause of health care–associated blood stream infections. Clin Infect Dis 2006 Mar 1; 42:647-56.
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