1162. A Snapshot of S. aureus Infections and Isolate Genotypes from the Dawn of the Community-Associated (CA-) MRSA Era, 1995-1997
Session: Poster Abstract Session: Staphylococcus aureus Infections in Children
Saturday, October 22, 2011
Room: Poster Hall B1
Background: In the 1990s, CA-MRSA strains emerged and have become the leading cause of skin and soft tissue infections (SSTI) in many populations.  The genotypic spectrum of MRSA and MSSA isolates obtained from children before 2001, when the USA300 strain became predominant, is not known.

Methods: A convenience sample of stored MSSA (n=46) and MRSA (n=27) isolates obtained from different children in 1995-97 at the University of Chicago Medical Center (UCMC) underwent genotyping.  Antibiogram, demographic and clinical data were abstracted.  Infections were classified as healthcare-associated (HA-) or CA-S. aureus by CDC clinical criteria. 

Results:  Patients had a median age of 4.6 years, 12% had only colonization, 63% had at least 1 chronic comorbidity, 55% were female, 63% African American, and 72% inpatients.  MSSA and MRSA patients did not differ significantly by any of these characteristics.  By CDC criteria, 22% (n=6) of MRSA and 20% (n=9) of MSSA were CA-S. aureus (p=0.8).  The Panton-Valentine leukocidin (pvl+) genes were carried by 59% (16/27) of MRSA, but only 2% (1/46) of MSSA isolates (p<0.0001).  Two isolates reported to be MRSA lacked mecA and were considered to be MSSA.  Of MRSA, only 5/25 (20%) carried SCCmec II, and 20/25 (80%) were clindamycin-susceptible.  MRSA isolates belonged to 6 multilocus sequence types (ST); 80% were ST1 (n=12) or ST8 (n=8).  MSSA included 16 ST; 75% were ST45 (n=10), ST30 (n=9), ST15 (n=8), ST5 (n=5) or ST8 (n=4).  All 12 ST1 and 5/8 ST8 MRSA isolates were pvl+ and carried SCCmec IV, consistent with USA400 and USA300, respectively.  USA300-type MRSA isolates were from 1 SSTI and 1 eye infection in previously healthy patients, and 1 each was from bacteremia, SSTI in a patient on steroids, and respiratory colonization.  USA400-type MRSA isolates were from SSTIs (n=6), empyema (n=1), lower respiratory infections (n=2), bacteremia (n=1), burn wound infection (n=1), and cervical lymphadenitis (n=1).

Conclusion: By 1997, among MRSA isolates obtained from children at UCMC, CA-MRSA strains likely already predominated.  USA400- and USA300-type isolates accounted for 68% of MRSA strains isolated.  HA-MRSA strains (SCCmec II-bearing and pvl-) were already being displaced by CA-MRSA as a cause of MRSA infections.  Few MSSA strains were pvl+. 

Subject Category: P. Pediatric and perinatal infections

Mary Acree, MD1, Michael Z David, MD PhD2, Diana Zychowski, BS3, Susan Boyle-Vavra, PhD3 and Robert S Daum, MD3, (1)Medicine, University of Chicago, Chicago, IL, (2) University of Chicago Medical Center, Chicago, IL, (3)Pediatrics, University of Chicago, Chicago, IL


M. Acree, None

M. Z. David, None

D. Zychowski, None

S. Boyle-Vavra, None

R. S. Daum, None

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