Abstract
Objective:
To report an outbreak of multi drug resistant Serratia infection in a tertiary level neonatal unit from eastern India.
Method:
Relevant data were retrieved from review of medical records. Standard methods for management of outbreak were carried out, and numerous infection control measures were implemented.
Result:
Out of the 6 reported cases of Serratia marcescens blood stream infections, majority were premature and all of them had a prior exposure to broad spectrum antibiotics. Most of the neonates (83.3%) survived. Median time of onset of symptoms was 22.5 (range: 2-83) days. Respiratory difficulty and thrombocytopenia were the most common presenting feature and laboratory abnormality observed.
Conclusion:
Serratia marcescens may lead to potentially serious outbreak neonatal unit. Prompt isolation of cases, Improving hand hygiene practice amongst healthcare professionals, limiting the use of broad spectrum antibiotics in NICU could help to contain the outbreaks to a large extent.
Introduction
Serratia marcescens is a gram negative bacillus belonging to Enterobacteriaceae family. It is often recognized as opportunistic pathogen causing nosocomial infections and outbreaks in critical care units including neonatal intensive care units.1,2 S. marcescens has been reported to be responsible for a wide range of infections which includes blood stream infections, pneumonia, wound infection, meningitis, endocarditis, ocular infections. 3 Typically, S. marcescens does not constitute part of the intestinal flora. The organism is known for expression of high level resistance to broad spectrum antibiotics including carbapenem. The organism is known to express intrinsic and acquired resistance to broad spectrum antibiotics.
Neonates admitted to neonatal intensive care units are at a high risk of acquiring various hospital acquired infections. Prematurity, low birth weight, use of invasive monitoring devices, respiratory support, central lines increases the risk of hospital acquired infections. Neonate may remain colonized with the organism for a long time prior to onset of clinical signs. S. marcescens has been reported to survive in the hands of healthcare workers for a prolonged period, which increases the risk of acquiring infection. 3 Various outbreaks of S. marcenscens infections in neonatal units has been reported in literature.3 -6 Prior exposure to broad spectrum antibiotics has been reported as a risk factor. 7 Clinical management of Serratia infections are often challenging, due to its inherent resistance to different classes of antibiotics. In addition, other acquired and adaptive mechanisms of resistance to various antibiotics have been reported. 7 The expression of Ambler class C β lactamase (Amp C), extended-spectrum β-lactamases (ESBL), Carbapenemase are chromosomally encoded and confer resistance to beta lactams, cephalosporins and carbapenem group of antibiotics.7,8
While carbapenems are increasingly used in neonatal units against gram negative sepsis, it could lead to opportunistic growth of Serratia species. The present outbreak describes the clinical and epidemiologic characteristics of admitted cases and may help clinicians for a better patient centered care, early identification and prompt infection control measures to contain an outbreak.
Materials and Methods
Study Design and Setting
This was a retrospective study, where 6 cases of systemic infections due to Serratia marscescens were documented during the month of April to May 2023 at a tertiary level neonatal intensive care unit (NICU) in eastern part of India. The NICU is a part of an university affiliated teaching hospital. The unit has 40 neonatal beds, and admits roughly 1200 to 1500 cases per year. The unit admits both inborn and outborn neonates and nearly 75% of the admitted cases are premature neonates. The NICU contains a total of 16 level 3 beds and is divided into 2 units and an isolation unit. Neonates with bacterial growth on blood culture and/or with strong clinical suspicion of systemic infection are isolated and managed in an isolation unit. These neonates are transferred back to the main NICU After clinical improvement or after the blood culture is reported negative.
Bacterial Isolation
During this outbreak, microbiogical detection was done by BacT/ALERT (BioMérieux, USA) automated system. VITEK 2 (BioMérieux, USA) automated system was used for Species identification. Antimicrobial susceptibility was reported. Minimum inhibitory Concentration (MIC) of antimicrobials were determined and reported. Additional susceptibility test was performed using Kirby–Bauer disk diffusion method and was reported as susceptible, intermediate and resistant.
At least 1 ml of diagnostic fluid was collected in a sterile manner and transferred to BacT/ALERT bottle. Bottles with positive growth were plated into Blood agar and MacConkey Agar plates and incubated overnight at 37°C (Figure 1). The colonies were analyzed by VITEK 2 Compact (BioMérieux, USA) automated system for species identification and antimicrobial susceptibility testing.
Growth of Serratia marcescens on MacConkey agar media.
Environmental Surveillance
As a part of outbreak evaluation, samples from NICU environment which includes Samples numerous surfaces, door handles, shelves, sinks, soap dispensers, weighing scales, bottle warmer, radiology equipment, hand sanitizer, ventilator circuits, humidifiers, stethoscopes and other medical equipments were collected. Standard methods and culture media were used for isolation of organism. Screening of healthcare professionals were also carried out by collecting samples from hand of caregivers.
We identified that our index case was an outborn neonate who presented with the Serratia meningitis, following this case, 5 new cases were reported. All 6 babies were studied for the presence of various risk factors and likely reasons to acquire Serratia infection. We also looked into the various positive blood culture isolates during this period.
Treatment Protocol
Any neonate with strong clinical suspicion of sepsis were managed as per unit protocol. Blood cultures were obtained prior to initiating antibiotic therapy. Lumbar puncture and CSF analysis (Cell count, sugar, protein, gram stain) including CSF cultures were obtained prior to starting antibiotics. Antimicrobial treatment was revised as per susceptibility report.
Data Collection
Medical records of admitted neonates were reviewed during this period. The relevant data of neonates with S. marscescens infection were collected, compiled and entered into a predesigned proforma in Microsoft excel. These variables encompassed demographic information, baseline characteristics, treatment received prior to Serratia isolation, presence of any risk factors for infection and their outcome.
Statistical Analysis
The collected data was summarized using descriptive statistics. Categorical variables were presented as frequencies and percentages, while continuous variables were reported as medians with interquartile ranges (IQR). Statistical analysis was performed using IBM SPSS Statistics 21 (SPSS Inc., Chicago, IL, USA).
Ethical Approval and Informed Consent
This research analyzed de-identified information from retrospective review of medical records which is exempt from ethics committee of institute. The authors followed EQUATOR Network guidelines during the conduct of this research project. Informed consent was obtained from the parents of all subjects
Result
A total of 6 neonates with Serratia blood stream infection were identified during this period. The baseline characteristics are presented in Table 1. Majority of the neonates were premature (66.7%) with median gestational age of 34.5 (range: 30-40) weeks and median birth weight 1675 (Range: 889-3700) g. In 83.3% of all cases, the onset of symptoms was beyond 72 hours of hospitalization, which suggests that the infections were acquired from the hospital (Table 2). The median time of onset of symptoms was 22.5 (range: 2-83) days. All neonates (83.3%) with onset of symptoms beyond 72 hours of life, had a prior exposure to broad spectrum antibiotics. Four neonates (66.7%) had a culture positive BSI prior to Serratia infection. Carbapenem resistant klebsiella was the causative organism in all the cases with prior culture positive blood stream infection and all the neonates received meropenem and colistin as a treatment.
Baseline Characteristics, Clinical Features and Risk Factors.
All neonates who received mechanical ventilation also received non-invasive ventilation. Central venous catheter includes umbilical venous catheter or peripherally inserted central venous catheter.
Characteristics of Individual Cases.
Worsening of respiratory status (66.7%) was the most common symptom noticed, followed by fever (50%), convulsion (33.3%), feeding intolerance (33.3%), lethargy (50%). Thrombocytopenia (Platelet count below 1 × 105/cmm) was the most common (83.3%) laboratory abnormality observed. Nearly one-third (33.3%) of cases had leukopenia (Total leukocyte count < 5000/cmm) and 66.7% cases had elevated acute phase reactants (C reactive protein > 10 mg/l). Neutropenia (Absolute neutrophil count < 1500/cmm) was observed in 16.7% of cases.
Environmental surveillance to identify potential reservoirs failed to identify any source. Cultures from floors, surfaces, water, humidifier chambers, ventilator circuits did not show growth of any pathogenic organism. On retrospective analysis of cases, we could identify the index case which was an out born neonate, who was admitted to the unit on day 19 of life. The neonate had a blood stream infection secondary to carbapenem resistant Klebsiella and was treated with Colistin and Tigecycline at an outside hospital. Blood culture at the time of admission, showed a positive growth of Serratia marsescens. The neonate also was found to have Pleocytosis and raised protein on CSF (Cerebrospinal fluid) analysis. CSF culture also revealed a positive growth of Serratia with similar antibiotic susceptibility pattern. The neonates was on mechanical ventilation prior to admission and during the course of treatment.
All 6 babies were studied for the presence of various risk factors and likely reasons to acquire Serratia infection. Half (50%) of the cases were outborn and received invasive mechanical ventilation prior to onset of symptoms and 50% had a central venous line for intravenous alimentation. We also looked into the various positive blood culture isolates during this period.
Following the sudden increase in BSI, following infection control measures were initiated.
Contact precautions for all cases of BSI
Strict isolation of proven cases of BSI
Environmental survey to identify the potential reservoirs
Supervision of hand hygiene practices of healthcare professional
Reinforcing the protocol for inserting central lines, maintaining ventilator circuits
Restricting number of visitors to NICU
Analysis of culture reports of the previous months.
Screening for carriage of Serratia was carried out and samples from hand of the healthcare personnel were sent, but none of the samples yielded a positive growth.
The antibiotic resistance pattern was relatively similar in all cases. Half (50%) of the isolates were resistant to aminoglycosides and quinolones. The incidence of carbapenem resistance was nearly 67%. All of the isolates were resistant to Polymyxin. One of the isolate was resistant to Tigecycline. All of the isolates showed susceptibility to cotrimoxazole. The cases were managed with susceptible antibiotics and supportive care. Five neonates received fluoroquinolone based regimen. Three (50%) received Meropenem and 2 (33.3%) received Tigecycline as part of treatment regimen. The details of antibiotic regimen used is depicted in Table 2. In addition, majority (83.3%) of the neonates required respiratory support during the course with 50% requiring invasive respiratory support.
After the infection control measures being taken, occasional sporadic cases of Serratia marcescens infection reported, but there has been no further documented outbreak in the unit till now.
Discussion
Serratia marcescens is an emerging nosocomial pathogen with a mortality rate of up to 44% in some series. However the epidemiological source of this pathogen is still unknown. This fact can be explained on the basis of ubiquity and resistance, this organism can survive in inanimate surfaces and even on antiseptic solutions for a long period of time. The organism is known to form biofilm and might be an important aspect in infection. Epidemic outbreak in NICUs are known to spread rapidly and are associated with significant morbidity and mortality.
There has been several outbreaks of Serratia infections reported in literature.9 -14 Majority of the reported outbreaks failed to identify the source of infections. Many sources of infection have been reported, which includes respiratory apparatus, humidifiers, donor milk etc.9,12 Premature neonates were affected more compared to term neonates in majority of the reported literature. The common clinical manifestation were blood stream infection.4,9,12 In some of the reported outbreaks, the investigators have performed screening of admitted neonates as a part of investigation of outbreak.9,12 Asymptomatic carriage has also been described in healthy neonates in NICU set up. The organism has been isolated from ET tip, ocular secretion, pharyngeal swab.9,12 Respiratory apparatus has been described as an important reservoir for the organism.12,14 Though the organism does not constitute a part of intestinal flora in neonates, Gastrointestinal tract may also become a reservoir during outbreaks. 14 In some of the studies, the organism has been isolated from stool samples from neonates admitted in NICU. 10
Cross contamination by the hands of care givers have been the predominant mode of transmission. 12 We also assume it to be mode of transmission in this outbreak, though we could not isolate the organism from hands of caregivers. All cases were isolated and hand washing practices were reinforced.
Respiratory worsening was the predominant clinical presentation observed in the current outbreak. Previous reported outbreaks and studies also suggest respiratory sign as one of the common clinical sign.4,12,14 In a recent outbreak of Serratia blood stream infection from a neonatal unit from Germany, almost two third of the affected neonates had respiratory sign, almost 80% had abdominal symptoms, 80% had thrombocytopenia. 4 In our study, we found significant thrombocytopenia (Total Platelet count below 1 × 105/cmm) in almost 83% of cases.
Serratia is intrinsically resistant to antimicrobials like penicillin, cephalosporin, tetracycline, macrolide, nitrofurantoin and colistin. 6 Over use of Carbapenem, Polymyxin might be one of the contributing factors for emergence of Serratia blood stream infection.
Genotyping of the isolates was not performed. Gene sequencing for identifying resistance gene was not performed. We have not looked into asymptomatic carriage or screening of other admitted neonates as a part of investigation during this period.
Conclusion
We infer from this study that, prompt infection control has led to termination of outbreak, however we were unable to trace the source of infection. Source of infection may not be identifiable in every outbreak. In addition to strict hygiene practice at the neonatal unit, antibiotic stewardship program is an important factor to limit emergence of outbreaks due to multidrug resistant organisms.
Footnotes
Acknowledgements
We acknowledge the support from Department of Micro-biology, IMS and SUM Hospital, Bhubaneswar during the study period.
Ethical Considerations
not required as it was a retrospective chart review and none of the subjects enrolled have been identified by name. The authors followed EQUATOR Network guidelines during the conduct of this research project. Informed consent was obtained from parents of all subjects.
Author Contributions
AM: Conceptualized, designed the study and collected data. DN: Analyzed data and prepared the initial draft. VK: Designed the study, revised the draft. RD: Supervision of data collection and analysis, critical input and revision of draft. All authors approved the final manuscript.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.