Rapid Eradication of a Cluster ofSerratia marcescensin a Neonatal Intensive Care Unit: Use of Epidemiologic Chromosome Profiling by Pulsed-Field Gel Electrophoresis

Serratia marcescens in the neonatal intensive care unit: A cluster investigation using molecular methods

BACKGROUND

Serratia marcescens (S. marcescens) is associated with nosocomial infections with significant morbidity and mortality in the neonatal intensive care units (NICU). We describe the control of a multi-clonal S. marcescens infections outbreak in our tertiary-level NICU and the application of molecular typing using repetitive element palindromic PCR (rep-PCR) and next generation sequencing (NGS) in the investigation.

METHODS

Outbreak investigation was performed where clinical, spatial and epidemiologic links were established. Screening of all infants in the NICU and the environment was performed. Rep-PCR and NGS methods were used to identify potential environmental sources of infections and clustering among cases.

RESULTS

Eleven cases were detected during the outbreak period: mean gestational age 27 weeks (range: 24-32), predominantly male (82%), mean age of infection 24 days (range: 6-51). Six infants were treated for conjunctivitis and one for bacteraemia. Identification of colonized infant via a point prevalence survey and cohorting of all infected/colonized patients were implemented. We performed environmental swabbing of surfaces, water outlets, chlorhexidine hand wash solutions and hand hygiene hand rubs. Both rep-PCR and NGS classified the 11 case isolates into 5 types. No point source was identified except for a single positive environmental isolate from a sink which was clonally distinct from the cases.

CONCLUSION

Identification and cohorting of infected/colonized patient was important in the control of S. marcescens outbreak in the NICU. The utility of rep-PCR was comparable to NGS in providing molecular information to develop S. marcescens outbreak control strategies.

Serratia marcescens Outbreak in a Neonatal Intensive Care Unit: New Insights from Next-Generation Sequencing Applications

Serratia marcescens is an environmental bacterium that is commonly associated with outbreaks in neonatal intensive care units (NICUs). Investigations of S. marcescens outbreaks require efficient recovery and typing of clinical and environmental isolates. In this study, we investigated how the use of next-generation sequencing applications, such as bacterial whole-genome sequencing (WGS) and bacterial community profiling, could improve S. marcescens outbreak investigations. Phylogenomic links and potential antibiotic resistance genes and plasmids in S. marcescens isolates were investigated using WGS, while bacterial communities and relative abundances of Serratia in environmental samples were assessed using sequencing of bacterial phylogenetic marker genes (16S rRNA and gyrB genes). Typing results obtained using WGS for the 10 S. marcescens isolates recovered during a NICU outbreak investigation were highly consistent with those obtained using pulsed-field gel electrophoresis (PFGE), the current standard typing method for this bacterium. WGS also allowed the identification of genes associated with antibiotic resistance in all isolates, while no plasmids were detected. Sequencing of the 16S rRNA and gyrB genes both showed greater relative abundances of Serratia at environmental sampling sites that were in close contact with infected babies. Much lower relative abundances of Serratia were observed following disinfection of a room, indicating that the protocol used was efficient. Variations in the bacterial community composition and structure following room disinfection and among sampling sites were also identified through 16S rRNA gene sequencing. Together, results from this study highlight the potential for next-generation sequencing tools to improve and to facilitate outbreak investigations.

Outbreak of Multidrug-Resistant Serratia marcescens Infection in a Neonatal Intensive Care Unit

Background.

Serratia marcescens causes healthcare-associated infections and significant morbidity and mortality in neonatal intensive care units (NICUs). We report the investigation and control of an outbreak of multidrug-resistant (MDR) S. marcescens infection at an NICU.

Methods.

An outbreak investigation and a case-control study were undertaken at a 36-bed NICU in a tertiary care hospital in Baltimore, Maryland, for the period from October 2004 through February 2005. The outbreak investigation included case identification, review of medical records, environmental cultures, patient surveillance cultures, personnel hand cultures, and pulsed-field gel electrophoresis (PFGE). The case-control study included case identification and review of medical records. Infection control measures were implemented. Eighteen NICU neonates had cultures that grew MDR S. marcescens during the study period. The case-control study included 16 patients with the outbreak strain or an unidentified strain of MDR S. marcescens and 32 control patients not infected and/or colonized with MDR S. marcescens, treated in the NICU for at least 48 hours during the study period.

Results.

PFGE analysis identified a single strain of MDR S. marcescens that infected or colonized 15 patients. Two patients had unique strains, and 1 patient's isolate could not be subtyped. An unrelated MDR S. marcescens isolate was recovered from a sink drain. Exposure to inhalational therapy was an independent risk factor for MDR S. marcescens acquisition after adjusting for birth weight. Extensive investigation failed to reveal a point source for the outbreak.

Conclusion.

A single epidemic strain of MDR S. marcescens spread rapidly and threatened to become endemic in this NICU. Transient carriage on the hands of healthcare personnel or on respiratory care equipment was the likely mode of transmission. Cohorting patients and staff, at the cost of bed closures and additional personnel, interrupted transmission and halted the outbreak.

Prolonged outbreak of Serratia marcescens in Tartu University Hospital: a case-control study

Background

The aim of our study was to investigate and control an outbreak and identify risk factors for colonization and infection with Serratia marcescens in two departments in Tartu University Hospital.

Methods

The retrospective case–control study was conducted from July 2005 to December 2006. Molecular typing by pulsed field gel electrophoresis was used to confirm the relatedness of Serratia marcescens strains. Samples from the environment and from the hands of personnel were cultured.

Results

The outbreak involved 210 patients, 61 (29%) developed an infection, among them 16 were invasive infections. Multivariate analysis identified gestational age, arterial catheter use and antibiotic treatment as independent risk factors for colonization and infection with Serratia marcescens. Molecular typing was performed on 83 Serratia marcescens strains, 81 of them were identical and 2 strains were different.

Conclusions

Given the occasionally severe consequences of Serratia marcescens in infants, early implementation of aggressive infection control measures involving patients and mothers as well as the personnel is of utmost importance.

Serratia infections: from military experiments to current practice

Serratia species, in particular Serratia marcescens, are significant human pathogens. S. marcescens has a long and interesting taxonomic, medical experimentation, military experimentation, and human clinical infection history. The organisms in this genus, particularly S. marcescens, were long thought to be nonpathogenic. Because S. marcescens was thought to be a nonpathogen and is usually red pigmented, the U.S. military conducted experiments that attempted to ascertain the spread of this organism released over large areas. In the process, members of both the public and the military were exposed to S. marcescens, and this was uncovered by the press in the 1970s, leading to U.S. congressional hearings. S. marcescens was found to be a certain human pathogen by the mid-1960s. S. marcescens and S. liquefaciens have been isolated as causative agents of numerous outbreaks and opportunistic infections, and the association of these organisms with point sources such as medical devices and various solutions given to hospitalized patients is striking. Serratia species appear to be common environmental organisms, and this helps to explain the large number of nosocomial infections due to these bacteria. Since many nosocomial infections are caused by multiply antibiotic-resistant strains of S. marcescens, this increases the danger to hospitalized patients, and hospital personnel should be vigilant in preventing nosocomial outbreaks due to this organism. S. marcescens, and probably other species in the genus, carries several antibiotic resistance determinants and is also capable of acquiring resistance genes. S. marcescens and S. liquefaciens are usually identified well in the clinical laboratory, but the other species are rare enough that laboratory technologists may not recognize them. 16S rRNA gene sequencing may enable better identification of some of the less common Serratia species.

Outbreak of neonatal infection by an endemic clone of Serratia marcescens

INTRODUCTION

The outbreak occurred between February and June 2006 and included identification of the cases, analysis of medical records, cultures from environmental sources, resistance analyses and genotyping profile of Serratia marcescens.

METHODS

The cultures were composed of 13 blood isolates, 17 rectal and hand swabs and air sampling.

RESULTS

The data obtained by pulsed-field gel electrophoresis exhibited three strains that contaminated 24 patients. Systemic infection was the most common in neonates with lower weight, long periods of hospitalization, premature delivery and the use of mechanical ventilation.

CONCLUSIONS

This investigation revealed the multifactorial nature of the outbreak. An endemic clone of S. marcescens was detected.

Serratia marcescens infections and outbreaks in neonatal intensive care units

Serratia marcescens is an important cause of hospital-acquired infections, especially in neonatal intensive care units (NICUs). This review analyzes clinical signs, risk factors, biotyping and sources of infection in newborns exhibited by this bacteria as well as the therapy which is commonly used and management. This review examines the reported cases of outbreaks of S. marcescens in NICUs published in pubmed over the last 10 years (key words: Serratia marcescens infections, outbreaks, Neonatal intensive Care Units). This report highlights the different prevention and control strategies employed in order to eradicate Serratia outbreaks in NICUs, including all healthcare procedures such as hand washing, introduction of alcohol-based antiseptic gel, enhanced cleaning and disinfection of medical equipment and wards, use of single-patient medical instruments, cohorting of colonized and infected infants, periodic screening cultures, earliest discharge of the infants.

Outbreaks of Serratia marcescens in neonatal and pediatric intensive care units: clinical aspects, risk factors and management

The following recommendations are derived from a systematic analysis of 34 Serratia marcescens outbreaks described in 27 publications from neonatal and pediatric intensive care units (NICU, PICU), in which genotyping methods were used to confirm or exclude clonality. The clinical observation of two or more temporally related cases of nosocomial S. marcescens infection should raise the suspicion of an outbreak, particularly in the NICU or PICU setting. Since colonized or infected patients represent the most important reservoir for cross transmission, hygienic barrier precautions (contact isolation/cohortation, the use of gloves and gowns in addition to strictly performed hand disinfection, enhanced environmental disinfection) should immediately be implemented and staff education given. Well-planned sampling of potential environmental sources should only be performed when these supervised barrier precautions do not result in containment of the outbreak. The current strategy of empiric antibiotic treatment should be reevaluated by a medical microbiologist or an infectious disease specialist. Empiric treatment of colonized children should use combination therapy informed by in vitro susceptibility data; in this context the high propensity of S. marcescens to cause meningitis and intracerebral abscess formation should be considered. In vitro susceptibility patterns do not reliably prove or exclude the clonality of the outbreak isolate. Genotyping of the isolates by pulse-field gel electrophoresis or PCR-based methods should be performed, but any interventions to interrupt further nosocomial spread should be carried out without waiting for the results.

Outbreak of Serratia marcescens in a neonatal intensive care unit: contaminated unmedicated liquid soap and risk factors

This study describes an outbreak of Serratia marcescens and its investigation and control in a neonatal intensive care unit (NICU). During a three-month period, five infants were colonised or infected by a single strain of S. marcescens. A case-control study, culture surveys and pulse-field gel electrophoresis analysis implicated a bottle soap dispenser as a reservoir of S. marcescens (P=0.032). Infants with S. marcescens colonisation or infection were also more likely to have been exposed to a central or percutaneous venous catheter (P=0.05) and had had longer exposure to endotracheal intubation (P=0.05). Soap dispensers are used in many hospitals and may be an unrecognised source of nosocomial infections. This potential source of infection could be reduced by using 'airless' dispensers which have no air intake for the distribution of soap. Prompt intervention and strict adherence to alcoholic hand disinfection were the key factors that led to the successful control of this outbreak.

Investigation of an outbreak of Serratia marcescens in a neonatal unit via a case-control study and molecular typing

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.