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Published on: January 27, 2019
Investigation of an outbreak of Serratia marcescens in a neonatal unit via a case-control study and molecular typing
N Deborah Friedman1, Despina Kotsanas, Judith Brett
1Department of Infectious Diseases, Southern Health, Monash Medical Centre, Clayton, Melbourne, Victoria, Australia. friedman.deb@gmail.com
Background:
In March 2004, infection or colonization with Serratia marcescens affected one third of all neonates in a newborn services unit (NBS).
Methods:
We performed a case-control study and automated ribotyping.
Results:
Forty-nine cases were compared with 64 controls. The overall mean length of stay (LOS) in the NBS was 67 days for cases and 36 days for controls, P = .005. Cases were of lower mean birth weight than controls (1566 g vs 1968 g, respectively, P = .02). Risk factors that trended toward significance for S marcescens acquisition included the following: premature rupture of membranes (odds ratio [OR], 2.7; 95% confidence interval [95% CI]: 1.0-7.1; P = .05), vaginal delivery at our hospital (OR, 2.1; 95% CI: 0.9-4.6; P = .06), intubation at delivery (OR, 2.3; 95% CI: 0.9-5.2; P = .05), mechanical ventilation (OR, 2.1; 95% CI: 0.9-4.4; P = .06), and theophylline treatment (OR, 2.5; 95% CI: 1.1-5.4; P = .02). Multiple logistic regression analysis revealed vaginal delivery at our hospital (OR, 3.4; 95% CI: 1.4-8.2; P = .007) and LOS >30 days (OR, 4.4; 95% CI: 1.8-10.6; P = .001) as independent risk factors for S marcescens acquisition. Ribotyping of specimens revealed 5 restriction patterns.
Conclusion:
Cases were of lower birth weight than controls, were born by vaginal delivery at our hospital, had longer LOS in NBS, and had greater requirements for respiratory support. Ribotyping of specimens revealed that this outbreak was not clonal.
Insights
Serratia marcescens infection in neonates was linked to lower birth weight and longer hospital stays. Vaginal delivery and extended length of stay were identified as key risk factors for acquisition.
Area of Science:
- Neonatal infections
- Infectious disease epidemiology
- Microbiology
Background:
- A significant Serratia marcescens outbreak affected one-third of neonates in a newborn services unit (NBS) in March 2004.
- This highlights the vulnerability of neonates to hospital-acquired infections.
Purpose of the Study:
- To investigate the risk factors associated with Serratia marcescens acquisition in neonates.
- To determine the clonal relatedness of the S. marcescens strains involved in the outbreak.
Main Methods:
- A case-control study was conducted comparing infected neonates (cases) with uninfected neonates (controls).
- Automated ribotyping was employed to analyze the genetic relatedness of S. marcescens isolates.
- Multiple logistic regression analysis identified independent risk factors.
Main Results:
- Cases had significantly lower mean birth weight (1566 g vs. 1968 g) and longer mean length of stay (LOS) in the NBS (67 days vs. 36 days).
- Independent risk factors for S. marcescens acquisition included vaginal delivery at the hospital (OR, 3.4) and LOS >30 days (OR, 4.4).
- Ribotyping revealed 5 distinct restriction patterns, indicating the outbreak was not caused by a single clone.
Conclusions:
- Neonates with S. marcescens infection were characterized by lower birth weight, vaginal delivery, prolonged NBS stay, and increased respiratory support needs.
- The non-clonal nature of the outbreak suggests multiple independent acquisition events or introduction from various sources.
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