Objectives Methicillin-resistant Staphylococcus aureus (MRSA) USA300 carrying Panton Valentine Leukocidin (PVL) genes has become the predominant cause of staphylococcal community-onset skin and soft tissue infections in our community. We assessed the molecular epidemiology of MRSA colonization and infection in our NICU.
Methods MRSA isolates recovered from surveillance cultures and selected clinical specimens were collected between 1993 and 2005. Beginning in September 2004, nares surveillance cultures were obtained from all patients admitted to the NICU (on admission and once weekly thereafter). Molecular typing of MRSA included pulsed-field gel electrophoresis (PFGE) and multiplex PCR. Medical records were abstracted; risk factors for PVL gene-positive CA-MRSA clones were assessed.
Results From 1993 through June 2005, a total of 14,786 surveillance cultures were obtained from NICU patients; 249 (1.7%) were positive, identifying 110 patients colonized with MRSA. Seven (1.1%) of 635 admission nares cultures of neonates were positive for MRSA (Sept 2004-Oct 2005); 4 of 7 were PFT USA300; 188 MRSA-positive specimens (144 surveillance and 44 clinical cultures) obtained from 133 patients 0-215 d after birth (mean 25, median 19 d) from 1993 through 2005 were analyzed by PFGE and PCR. PVL+ USA300 CA-MRSA strains were never seen in the 1990s and first appeared in 2001, increasing significantly in proportion from 20% of MRSA isolates recovered in the NICU to 60% in 2004 and 2005 (p = .04) (Figure). Risk factors significantly associated with the recovery of PVL+ CA-MRSA USA300 isolates in univariate analysis included shorter length of stay, older gestational age, and higher birthweight; older gestational age was an independent predictor in multivariate analysis (OR 1.25/week, 95% CI 1.0-1.6). Mode of delivery (cesarean section vs vaginal delivery) was not associated with PVL status of the MRSA isolate.
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