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Reduced chlorhexidine susceptibility in NICU-acquired versus externally acquired coagulase-negative staphylococci isolates

Presented at the Neonatal Society 2018 Autumn Meeting.

Sethi D1,2, Faust K3, Kiy C3, Clarke P2,4, Härtel C3, Rupp J5, Webber M1,2

1 Quadram Institute Bioscience, Norwich Research Park, UK
2 Norwich Medical School, University of East Anglia (UEA), UK
3 Department of Paediatrics, University of Lübeck, Germany
4 Neonatal Unit, Norfolk and Norwich University Hospitals, UK
5 Department of Infectious Diseases and Microbiology, University of Lübeck, Germany

Background: Coagulase-negative Staphylococci (CoNS) are the main cause of late-onset sepsis in the NICU. Good skin antisepsis prior to central catheterisation can reduce catheter colonisation. Using lower antiseptic concentrations may mitigate the risk of chemical burns in neonates, but little is known about whether this affects the antiseptic tolerance of CoNS. We investigated whether CoNS isolated from two NICUs using two different antiseptics would show differences in susceptibilities to either antiseptic. Our hypothesis was that CoNS isolates would show reduced susceptibility to the antiseptic being used preferentially at the NICU where they were collected.

Methods: Longitudinal prospective surveillance study collecting weekly skin swabs for 3-months from i) all neonates in a UK NICU using chlorhexidine gluconate (CHG); ii) neonates <1500g admitted to a German NICU using octenidine dihydrochloride (OCT). Skin swabs were collected on admission and weekly thereafter. We determined minimum inhibitory concentrations (MICs) to CHG and OCT for Staphylococci using agar dilution. Isolates from admission swabs were considered to be ‘externally-acquired’ while those isolated from the subsequent weekly surveillance swabs were considered to be ‘NICU-acquired’. Ethics approval was obtained in Lübeck and was not required in the UK.

Results: Susceptibility to CHG and OCT was determined for all 863 UK and 411 German isolates. UK isolates had a significantly greater tolerance to CHG compared with German isolates (Fig.1). Although MICs to OCT were similar for isolates from both units, more isolates with highly elevated OCT MICs originated from the OCT-naïve UK unit. UK CoNS isolates collected on admission to NICU were more susceptible to CHG than those collected from weekly screening during the admission (Fig. 2); this was not seen in the German unit.

Conclusion: Widespread CHG use may select for CHG tolerance in CoNS. The reduced susceptibility of isolates acquired on admission (externally acquired) compared with those from weekly screening (NICU acquired), suggests tolerant strains are being selected for, and are more prevalent, in NICU. Further work is required to investigate the possibility of transmission between infants. A better understanding of the ecology of CoNS in NICUs and of the relationship between antiseptic use and tolerance is required to guide antiseptic usage policy in the NICU.

Corresponding author: D.Sethi@uea.ac.uk

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