Risk factors for Staphylococcus capitis pulsotype NRCS-A colonisation among premature neonates, Neonatal Intensive Care Unit, Dunedin Hospital

Abstract

Coagulase-negative staphylococci (CONS) are the most common cause of bloodstream infections in neonatal intensive care units (NICUs). S. capitis, a species of CONS, has recently emerged as a common cause of neonatal disease, in some NICUs causing up to 40% of all bloodstream infections. A clone of S. capitis called NRCS-A, which is multidrug resistant and capable of persistence in NICUs, has been isolated from neonates worldwide. Most studies of S. capitis NRCS-A have focused on the genome structure, or risk factors for bloodstream infection. We conducted both a retrospective and prospective study among neonates admitted to the Dunedin Hospital NICU to investigate the risk factors of S. capitis skin colonisation and transmission.

Our studies used the results from an ongoing Dunedin Hospital NICU S. capitis surveillance system. We collected data on baseline and weekly neonatal exposures, along with S. capitis surveillence test results. We collected weekly data on exposures such as medication use, medical history, procedures and devices, enteral feeds, weight, type of beds, and bed spaces. Additionally the prospective study collected weekly data on family and staff contact.

The retrospective study analysis categorised participating neonates each week as a case or a control depending on whether the neonate became colonised with S. capitis or remained non-colonised, respectively. We matched control data to case data based on calendar time. A nested case-control analysis with conditional logistic regression was used to investigate the differences between cases and controls for baseline and weekly exposures. A full analysis of the ongoing prospective study will be performed when data collection is complete.

A progress report of the prospective study described the baseline characteristics of the 13 participants: 1 case and 12 controls. Our retrospective study nested-case control analysis included 26 cases and 203 controls.

Factors associated with an increased risk of S. capitis colonisation included oral sodium chloride use (OR 6.1, 95% CI 1.4-27.1, p=0.02), diagnosed patent ductus arteriosus (OR 2.9, 95% CI 1.1-7.9, p=0.04), diagnosed chronic lung disease (OR 4.8, 95% CI 1.1-22.3, p=0.04), and requirement of invasive mechanical ventilation (OR 3.4, 95% CI 1.1-10.4, p=0.03).

Factors associated with decreased risk of S. capitis colonisation included being born as a part of a multiple birth (OR 0.14, 95% CI 0.04-0.40, p=<0.001), having an area of inflamed skin (OR 0.31, 95% CI 0.13-0.70, p=0.005), having an inflamed axilla (OR 0.31, 95% CI 0.13-0.70, p=0.005), and enteral feeds with formula (OR 0.29, 95% CI 0.08-0.99, p=0.05).

We found that co-morbidities, such as patent ductus arteriosus and chronic lung disease, or devices, such as invasive mechanical ventilation, were associated with an increased risk of S. capitis colonisation. Having an inflamed axilla, and antimicrobial use were independently more common among neonates that ever became colonised than neonates that never became colonised, although in the nested case-control analysis neither were associated with a statistically significant increased risk of S. capitis colonisation. Overall, our retrospective study showed that neonates with comorbidities, which may require more management by medical staff and equipment, were associated with an increased risk of S. capitis colonisation.