Serratia marcescens (S. marcescens) is a Gram-negative bacillus belonging to the Enterobacteriaceae family. It can form part of the human microbiota but is also found in inanimate reservoirs poor in nutrients,1 including in hospitals, such as wash-hand basin taps,2 intravenous fluids3 and baby shampoo.4 These reservoirs can sometimes be the source of nosocomial outbreaks.

The Río Hortega University Hospital in Valladolid is a public 680-bed tertiary referral hospital serving a population of approximately 256,000. The incidence of S. marcescens bacteraemia here is very low; three episodes in 2013 and one up to the end of October 2014, all of nosocomial origin. Alarms were therefore raised in the last week of November 2014, when there was an increase in the incidence of S. marcescens isolates in blood cultures.

All the affected patients had been seen in Accident and Emergency (A&E), the isolates had the same antibiogram, and there was little or no relationship between the isolation and the patients’ initial symptoms. Over the ensuing days, S. marcescens continued to be isolated in samples not only from A&E patients, but also from patients in the ICU, where there was an outbreak involving 16 patients that lasted a month.

At the request of Microbiology, the hospital's Medical Management set up a multidisciplinary committee to coordinate an epidemiological and microbiological investigation into the outbreak, taking guidance from the literature on the subject.5–7 The results of the investigation were to enable measures which, in the end, brought the outbreak under control.

The outbreak cases were defined as patients with isolation of S. marcescens in a clinical sample with a characteristic antibiogram since 21 November 2014, including both colonisation and infection. Colonisation was considered when there were no associated symptoms or specific treatment, and infection when there was isolation in patients with compatible symptoms in whom specific antibiotic treatment was prescribed.

From 21 November 2014, the Microbiology Laboratory began to detect an increased incidence of S. marcescens isolates recovered from blood cultures. The first three were from patients who had been seen in the paediatric and adult A&E Departments. The isolates had the same antibiogram, but the correlation of the microbiological findings with the patients’ symptoms was scant or non-existent.

The antibiograms of these first three cases showed distinctive features; our automated system found an MIC of 2μg/ml for ertapenem, and 0.5μg/ml for imipenem, the result of which was that the expert system suggested it might be a strain that expresses a chromosomal class A carbapenemase, SME (Fig. 1). Study of the strains by E-test indicated that they were susceptible to ertapenem (MIC 0.25mg/l).

Fig. 1.

Identification of the first strain, automated antibiogram and interpretation by the expert system.

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The distinctive features of these isolates were brought to the attention of the clinical departments involved so they could be carefully assessed. On 3 December, the hospital's Medical Management set up an interdisciplinary committee (paediatric and adult A&E departments, Microbiology, Preventive Medicine, Hospital Pharmacy, Nursing Directorate and Medical Management) to analyse the findings periodically and decide on the measures to be adopted.

Control of the outbreak

At the meeting on 11 December (12 cases), it was decided to withdraw Bohmclorh® 2% aqueous chlorhexidine from the entire hospital and replace it with another product.

That same day, the Hospital Pharmacy Service sent the alert to the Spanish Agency of Medicines and Medical Devices (Agencia Española de Medicamentos y Productos Sanitarios, AEMPS).

Over the following days, four more cases were detected. On further investigation, it was found that Bohmclorh® 2% aqueous chlorhexidine had not been completely withdrawn from the entire hospital.

On 19 December, the AEMPS issued an alert (ref. COS 2/2014) (Fig. 2) reporting the withdrawal of lots i-34 and i-35 of the antiseptic product Bohmclorh® 2% chlorhexidine aqueous solution 250ml from the market because they were contaminated with S. marcescens.

Fig. 2.

Informative note from the Spanish Agency of Medicines and Medical Devices.

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On 23 December we received the results of the molecular epidemiology tests carried out at the Spanish National Microbiology Centre (Fig. 3), which showed that the strains in both the clinical samples and the chlorhexidine packaging belonged to the same clone.

Fig. 3.

Dendrogram of some of the strains of Serratia marcescens involved in the outbreak. Report from the Spanish National Microbiology Centre received on 23 December 2014.

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On 30 December after a week with no cases, the outbreak was declared resolved.

The possibility of the emergence of infections, including epidemic outbreaks, resulting from contamination of materials used in healthcare is a known and accepted fact nowadays in the management of infectious diseases. This includes antiseptic solutions, which are not exempt from contamination by different resistant microorganisms. Among others, there have been reports of cases associated with povidone iodine, benzalkonium chloride and chlorhexidine.7,9–12 This article describes an outbreak of S. marcescens infection originating from Bohmclorh® 2% aqueous chlorhexidine solution, a disinfectant used in our hospital for cleaning the skin prior to the extraction of blood samples for blood culture or insertion or maintenance of vascular catheters.

The systematic review of microbiological isolates in the Microbiology Laboratory, especially those corresponding to sterile samples, and the low rate of S. marcescens bacteraemia in our hospital meant that we were quickly alerted to the possibility that we had an outbreak. The fact that the microorganism concerned was not a common cause of bacteraemia in the affected centre rapidly led us to suspect an outbreak and to investigate its origin. Some published studies report delays of up to a month in the detection of an outbreak as a consequence of inadequate monitoring of changes in the prevalence of certain microorganisms.7

Such reports should serve to underline the importance of keeping protocols for action and prevention of nosocomial infection, and the training and commitment of healthcare personnel, in terms of their compliance, continually up-to-date. In almost all outbreaks of this type, deficiencies have been discovered in the protocols for prevention and in compliance with them. Certain articles in the literature report errors in the chlorhexidine concentration used, i.e. lower than that recommended by the centre's protocols.7

Also important is good coordination among the departments involved and close monitoring of how the outbreak evolves. In our case, the intervention of the Hospital's Medical Management, which, after being informed about the suspected problem and its potential importance, immediately organised the setting up of an interdisciplinary committee to coordinate the epidemiological investigation and propose the measures to be adopted, made a decisive contribution to the control of the outbreak.

Systems must also be in place to allow rapid adoption and implementation of committee decisions by healthcare personnel. Since these outbreaks are often associated with materials and products involved in nursing care, it is important that nursing staff are also involved in monitoring the implementation of these measures. In fact, in our case, failures and delays in this area were what led to the appearance of new cases after the order to withdraw chlorhexidine.

However, even when the suspicion is acted on and the approach to these episodes is rapid and effective, it is very difficult, as in this case, to avoid an increase in costs for both the patient and institution deriving from antibiotic treatments and other diagnostic tests and therapeutic measures which sometimes also prolong the hospital stay.

Lastly, the role of referral centres which are often involved in the identification and control of these epidemic outbreaks is crucial, especially when, again as in this case, they affect several centres some geographical distance apart belonging to different health services. The participation of this type of centre is important for the coordination of efforts to identify the origin of the outbreak and in the dissemination of information to the affected centres. In our case, the role of the Spanish National Microbiology Centre (Dr Vindel) was instrumental in this regard, confirming the clonal origin of the outbreak and facilitating the exchange of information between the different affected centres, some of which have also recently published their experience.13–15

The authors declare that they have no conflicts of interest and that this study has received no funding.