Methods: From May 2015-March 2016, we prospectively collected nasal swabs from 536 neonates <28 days of age admitted from the community, perinatal services, or other hospitals. SA isolates were characterized by multilocus sequence type (MLST), staphylococcal chromosomal cassette mec (SCCmec) type, agr, spa-type, cytotoxicity and superantigen (SAg) genes. The characteristics of MRSA vs. MSSA and infecting vs colonizing isolates were compared using Mann Whitney U and Fisher’s tests. Logistic regression was used to compare characteristics of infants colonized vs uncolonized with SA.
Results: We identified 96 (18%) and 23 (4%) neonates with SA colonization and/or infection on admission. Among the 96 colonized infants, 28 had MRSA and 68 had MSSA. ST59-SCCmecIVa-t437-agr-1 (20/28, 71%) and ST188-t189-agr-1 (11/68, 16%) were the common colonizing MRSA and MSSA clones, respectively. Among 23 isolates associated with infection, 17 were MRSA and ST59-SCCmecIVa-t437-agr-1 (6/17, 35%) was also the most common clone. Of the 119 SA isolates, 108 (91%) contained at least one SAg gene; however, none carried sasX. Cytotoxicity was significantly different among the main clones (p=0.04). While MRSA and MSSA had similar cytotoxicity (83.7% vs 85.9%, p=0.45), infecting isolates had higher cytotoxicity than colonizing isolates (87.6% vs 84.5%, p<0.01). Female sex (ORADJ=2.05, p<0.01), age >7 days (ORADJ=7.14, p<0.01), and vaginal delivery (ORADJ=2.16, p<0.01) were RFs for SA colonization, while antibiotic use was protective (ORADJ=0.25, p<0.01).
Conclusion: SA colonization was common in infants admitted to our NICU and 2 clones predominated. MRSA and MSSA did not differ in cytotoxicity, although infecting isolates had higher cytotoxicity. Several non-modifiable risk factors for SA colonization were identified. Our results suggest that screening infants for SA is useful and interventions to target cytotoxic clones should be explored.
A. Hill-Ricciuti, None
Y. Qi, None
L. Saiman, None
A. C. Uhlemann, Merck: Investigator , Grant recipient .