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Molecular detection of enteric pathogens: clinical and economic impact

Rapid molecular testing for enteric bacteria should increase diagnostic accuracy and reduce time, material and labour 
Dave Thomas FIBMS
Nicki Hutchinson MBBS MSc FRCPath
Microbiology Department, 
Hampshire Hospitals NHS Foundation Trust,
Basingstoke, UK
Annie Jones MSc MBA
Magus Strategic Communications Ltd, 
Old Malton, UK
Infectious intestinal disease (IID) is a common condition. Vomiting and/or diarrhoea are the most common symptoms, but fever, stomach pains and bloody stools may also be present. There are an estimated 17 million cases of IID reported annually in the UK,(1) and a recent UK study reported rates of 274 cases per 1000 person-years.(1) Surveillance data from the Health Protection Agency between 1992 and 2000 on more than 5000 outbreaks of IID in England and Wales reported that 27% of outbreaks occurred in the hospital setting.(2) These outbreaks are associated with significant costs in terms of ward closures for new admissions, isolation beds and staff absence. Indeed, one UK hospital Trust has reported annual costs of £1.49 million (April 2002 to March 2003) in terms of unit closures to new admissions.(2)
Current guidelines recommend the isolation of patients admitted to hospital with diarrhoea until laboratory results are available using a syndromic approach to testing.(3) However, between 4% and 70% of patients in hospital outbreaks of IID test negative for all pathogens, and failure to rapidly identify these patients represents a considerable drain on resources.(2) Laboratory testing for the infectious pathogens is also often conducted sequentially. The unnecessary isolation of patients without an infectious cause of their diarrhoea and delay in obtaining an accurate diagnosis are factors contributing to the associated costs. 
Historically, the principle diagnostic modalities for IID have included culture, microscopy and antigen-based tests. Culture methods are slow and often have low sensitivity in the presence of antibiotic use. Antigen testing assays are costly and only exist for a limited number of pathogens. As causative pathogens can be viral or bacterial, IID is well suited for automated multiplex molecular testing,(4) which has an emerging role in the diagnosis of diarrhoeal disease. 
In conjunction with molecular testing for Norovirus and Clostridium difficile, a decision was made in 2013 to introduce the BD MAX™ Enteric Bacterial Assay (BD Diagnostics, Oxfordshire, UK) for the screening of diarrhoeal admissions in the Hampshire Hospitals NHS Foundation Trust. The Trust serves a population of approximately 600,000 across Hampshire and parts of west Berkshire. Between 2012 and 2013, 59,000 patients received planned inpatient or day care treatment by the Trust. 
In the winter months, the Trust screens all diarrhoeal admissions. Patients are isolated until laboratory results are available. The decision to introduce the system was based on the fact the system is fully automated, has a time to result of less than three hours and includes the common major bacterial pathogens associated with IID (Table 1): Salmonella spp, Campylobacter spp, Shigella spp (including S. dysenteriae serotype 1 strains containing the stx gene), Enteroinvasive Escherichia coli (EIEC) and Shiga toxin-producing Escherichia coli (including O157).
The addition of the BD MAX™ Enteric Panel to the screening of diarrhoeal admissions to the hospital during the winter months has enabled results to be made available to the clinical staff within three hours. Patients testing negative can be admitted to general wards freeing up isolation beds. Over the first year of testing, it is estimated that more than 2000 isolation bed days have been saved. It is estimated that a hospital bed costs between £225 to £400 per day (…) with an estimated cost saving with the reduction in isolation beds to the Trust of between £450,000 and £800,000.
Accurate diagnosis of IID means appropriate antibiotics can be started quickly if clinically indicated, and improves antibiotic stewardship. In many cases, rapid diagnosis allows patients to be discharged to home or community care more quickly, again easing the pressure on hospital beds. Reducing the amount of time that patients spend in isolation has many other benefits, including reducing anxiety and improving the overall patient experience.
Case study
A 40-year-old man with profuse diarrhoea and abdominal pain was admitted to the surgical ward isolation bed and started on ciprofloxacin for gastroenteritis. In less than 24 hours, he was discharged home on clarithromycin for PCR-positive Campylobacter. The rapid panel allowed us to ensure this patient was on the correct treatment within 24 hours as well as releasing an isolation bed.
Prior to the introduction of the BD Max Enteric Bacterial Panel, the turnaround time (TAT) to obtaining results would have taken a minimum of 48 hours. The reduction in TAT means that automated runs can take place twice per day when necessary, enhancing the planned workflow for the laboratory. The automated system has proved simple to use, with minimal training necessary for laboratory staff. In addition, rapid identification of the causative pathogen in outbreak situations means that they can often be contained on a single ward or clinical area, reducing the need to restrict admissions and close beds.
Editorial support was provided by
BD Diagnostics, Oxfordshire, UK.
Declaration of interest
AJ works as an independent scientific consultant to a number of bodies and pharmaceutical companies, including the British Society for Antimicrobial Chemotherapy, International Society for Chemotherapy, Becton Dickinson (Diagnostics), Novartis (Anti-Infectives), Astellas (Anti-Infectives), Smith & Nephew (Wound Care), Wyeth and Pfizer (Anti-Infectives and Vaccines). DT is the Microbiology Manager Hampshire Hospitals NHS Foundation Trust. NH is a consultant Microbiologist and the 
clinical director for pathology for HHFT. She has previously spoken at a BD-sponsored symposium.
  1. Tam CC et al. Longitudinal study of infectious intestinal disease in the UK (IID2 study): incidence in the community and presenting to general practice. Gut 2012;61(1):69–77.
  2. Lopman BA et al. Epidemiology and cost of nosocomial gastroenteritis, Avon, England, 2002–2003. Emerg Infect Dis 2004;10(10):1827–34.
  3. Public Health England. UK Standards for Microbiology. Gastroenteritis and Diarrhoea. Standards Unit, Microbiology Services, PHE;2013.
  4. Platts-Mills JA, Operario DJ, Houpt ER Molecular diagnosis of diarrhea: current status and future potential. Curr Infect Dis Rep 2012;14(1):41–6.