Risk factors for Staphylococcus capitis pulsotype NRCS-A colonisation among premature neonates in the neonatal intensive care unit of a tertiary-care hospital: a retrospective case-control study

BACKGROUND: A S. capitis strain called NRCS-A (S. capitis NRCS-A) has emerged as a cause of bloodstream infections and sepsis in neonatal intensive care units (NICUs) worldwide. AIM: To identify risk factors for S. capitis NRCS-A colonisation among neonates, Dunedin Hospital NICU, Dunedin, New Zealand, from September 2013 through March 2015. METHODS: Weekly axillary swabs categorised eligible neonates as a case or a control. A case was defined as a week ending with a neonate's first positive swab for S. capitis NRCS-A and a control as a week in which a neonate remained negative. Weekly exposures were abstracted from hospital medical records. Analyses were performed using conditional logistic regression. FINDINGS: The median (range) gestational age at birth of participants was 32.7 (23.1–41.3) weeks. Participants contributed 26 weeks of case data and 177 weeks of control data. On adjusted analysis compared with matched controls, cases had higher odds of requiring invasive mechanical ventilation (OR 3.6, 95% CI: 1.1–11.6, p=0.035) and of a patent ductus arteriosus (PDA) (OR 3.0, 95% CI: 1.0–9.0, p=0.044). Cases had lower odds of being part of a multiple birth (OR 0.24, 95% CI 0.08–0.73, p=0.001), having an area of inflamed skin (OR 0.31, 95% CI: 0.13–0.75, p=0.009), and specifically an area of inflamed axillary skin (OR 0.08, 95% CI: 0.01–0.50, p=0.006). CONCLUSIONS: We found that premature neonates with invasive mechanical ventilation and PDA had greater odds for S. capitis NRCS-A colonisation. Transmission may be mediated by increased staff contact, but prospective research is needed to confirm this.