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Faeces samples

This page explains the necessity for appropriate clinical details, sample volumes required and gives information about specific tests that are carried out in this department.

Contents:

Routine faeces culture 

What clinical details should I provide?

Please note that faeces culture is a highly specialised series of tests that involves screening a sample for a number of bacterial pathogens causing gastroenteritis.  Therefore our laboratory requires clinical information to select the appropriate tests.  Please include as much information as possible regarding:

  • The patients history: For hospital patients: if the patient had diarrhoea upon admission or shortly after (within 48 hours of admission) and for GP patients: If the patient has a recent history of hospital admission

  • If you think the patient’s symptoms are related to something they ate/ drank.

  • If the patient is immunocompromised e.g. neutropaenic, HIV patient.

  • If the patient has been admitted because of diarrhoea, abdominal pain.

  • If the patient has a history of GI disorders.

  • If the patient been exposed to untreated water (sewage) or animals.

  • If other members of the patients family have symptoms of gastroenteritis

  • If the patient has been involved in a community outbreak of diarrhoea.

 

What volume of sample should I collect?

The department requires a minimum of 5ml of faeces collected into a 30ml sterile universal or blue top with 'spoon' for processing.  Please note also that samples should be fresh (ideally sent up to the laboratory within 2-3 hours of being passed). 

If faeces contaminated with urine then M, C & S, parasitology and Clostridium difficile investigations can be tested but this may affect the result.

For full Faeces collection advice please click here

What does faeces culture Include? 

Culture for enteric pathogens Includes:  Campylobacter species, Salmonella species and E. coli O:157 in all cases of non-hospital acquired diarrhoea.  The department also screens for Shigella species in all patients with a history of foreign travel.  We also screen for Vibrio cholerae in patients with a history of travel to Cholera endemic areas AND if the patient has a liquid stool.   We screen for Vibrio parahaemolyticus in patients with a history of shellfish consumption or participation in water related activities.  Lastly, the department also cultures for Yersinia enterocolitica in patients with symptoms suggestive of Yersiniosis (especially young or elderly patients with mesenteric lymphadenitis, pseudoappendicitis, terminal Ileitis).

What happens if I don’t provide suitable clinical information?

Samples will not be cultured unless appropriate clinical information is provided.   The Microbiology department deals with a large volume of samples; therefore it is vital that sufficient clinical details are provided to establish the cause of diarrhoea as being unrelated to C. difficile.

 Which samples are cultured regardless of clinical information?

All GP samples and the following wards/ departments will receive faeces culture (If requested) regardless of clinical Information.

Emergency department, MAU, ICU, SAU, CDU, all paediatric wards, all outpatient wards/ clinics wards 305 and 304.  The microbiology department wil also check samples from other inpatient wards WHERE CULTURE HAS BEEN REQUESTED, for admission dates.  Samples from patients who have been in hospital for less than 3 days will also be cultured.

Travel associated diarrhoea

What clinical details should I provide?

Travel to foreign countries may result in infectious diarrhoea being attributed to more unusual pathogens not seen (or seen rarely) in the UK.  Faeces foreign travel investigation includes additional culture methods and additional microscopy for faecal parasites.  It is vital that if a patient has been abroad to provide as much information as possible such as:

  • Where has the patient been?

  • How long ago?

  • How long have they had their symptoms (this is especially important for determining what tests are performed, as protracted diarrhoea is a common feature of infection with intestinal parasites).

  • Is the patient immunocompromised?

  • If ?High Risk pathogen suspected, please indicate, so we can process the sample using the correct safety procedures.

Which parasites will the department screen for?

In the laboratory, provided the relevant clinical details are given, we will look for Helminths (worms) e.g. Ascaris, hookworm, tapeworm, liver flukes and other Helminths.  We will also look for Protozoan parasites e.g. Giardia, Cryptosporidia, Entamoeba and others.

What happens if I don’t provide suitable clinical information?

Please note that samples will not be examined for ova, cyst’s and parasites unless appropriate clinical information is provided.  The microbiology department deals with a large volume of samples; therefore it is vital that in these cases, sufficient clinical details are provided to establish the cause of diarrhoea as being unrelated to C. difficile.

 

Clostridum difficile testing

When will the sample be tested?

The microbiology department currently processes faeces samples for C. difficile investigations on a 7 day basis.

Monday - Friday: 2 runs are performed in the day (am and pm).  Samples must reach pathology reception by 9am at the latest for the morning run and 12.30pm for the afternoon run.

Saturday - Sunday: 1 run is performed each day.  Samples must reach pathology reception by 9am at the latest.

********From April 2012 the Department of Health have issued a new mandatory 2 stage testing algorithm for Clostridium difficile********

Click for link to Department of Health information

Test information

C. difficiie is an opportunistic anaerobic spore forming bacteria present in the intestines. It can produce toxins which results in infection. Some strains do not produce toxins but the bacteria being present can mean that the patient has the potential to excrete it and have an increased risk of developing the infection and diarrhoea.

This method will differentiate between patients who have active C. difficile infection and those that could be at risk of becoming infected (excretors).

This new method aims to provide more effective and consistent diagnosis across the NHS. The 2 stages include:

  • Stage 1 – A test to detect the presence of C. difficile

  • Stage 2 – a more specific test for detecting toxin A&B produced by C. difficile infection.

Please see the PDF document for the 2 stage testing algorithm:

2 stage C. difficile algorithm 

GDH: Glutamate dehydrogenase (GDH) is an enzyme produced in large amounts by both toxin and non-toxin producing C. difficile.

Toxin A&B: C. difficile can produce 2 toxins A and B. They are responsible for causing infection and diarrhoea.

CDI: C. difficile infection

Results interpretation
  • For samples that are C difficile GDH negative.

The comment will be:

‘Diarrhoea is unlikely to be attributed to C difficile.  If there is still a high clinical suspicion of C difficile infection, please discuss this with a Consultant Microbiologist’.

 These samples will not be tested for C difficile toxin.

The comment will be:

'C.difficile toxin not tested.  As part of the Department of Health's Two Stage Testing protocol, toxin testing is only carried out on patients who are GDH positive.'

  • For samples that are C difficile GDH positive and C difficile Toxin negative.

 The comment will be:

'A GDH positive result indicates colonisation of the gut with the Clostridium Difficile bacterium.  The absence of toxin A & B means Clostridium difficile infection (CDI) is unlikely.  Please be extra vigilant when prescribing antibiotics and ensure the patient remains in isolation if their diarrhoea continues.  The Microbiology department no longer requires repeat samples to confirm GDH Positive Toxin Negative results.'

  •  For samples that are C difficile GDH positive and C difficile Toxin positive.

 For Inpatients:

'Confirms C.difficile toxin associated disease/ diarrhoea. Clearance specimen for C.difficile not indicated RDH prescribers - check guidance on CDI management.  This can be found on the website below.  http://flo/depts/clinical/pathology/microbiology/antibiotic-guidelines/treatment-cdad/'

For GP patients:

'Confirms C.difficile toxin associated disease/ diarrhoea. Clearance specimen for C.difficile not indicated.  PCT prescribers - check guidance on CDI management.  This can be found on the website below.  http://www.derbyshiremedicinesmanagement.nhs.uk/clinical_guidelines/prescribing_guidelines'

Test ordering:

ICM users will now see the test as:

Faeces (C. difficile screen only)

The is no change for other electronic users. IF an electronic ordering system is not available please request 'C. diff screen'

What volume of specimen is required and when should it be taken?

A minimum of ¼ of a pot of faeces of Bristol stool type 6 or 7 must be submitted for testing. 

Samples must be sent immediately (within 2 hours) to the lab (a delay in transport can result in a significant loss of any toxin that may be present in the sample).  Samples that cannot be processed within two hours must be refrigerated (up to two days).

Please consult Infection Control for guidance as to when to submit samples per episode of diarrhoea.

What is the department’s policy on not testing samples?

Please be aware of our criteria for not testing of stool samples for C difficile toxin. 

  • If the sample is not Bristol Stool Type 6 or 7 it will not be tested (is the stool liquid enough for pippeting).

  • If the sample is entirely mucus it will not be tested as our current method for testing is validated for faeces only.

  • If the sample is from patients under 2 years of age. *

  • If the patient has tested positive within 28 days. *

  • If more than one stool has been sent per episode of diarrhoea (7 days) the second and subsequent samples will not be tested until a period of 7 days has elapsed from the last recorded sample. *

 * Samples may be processed but only after clearance from a consultant microbiologist or the Infection Control Team.

 

Virology   

What are the indications for testing a sample for enteric viruses?

Most people with viral gastroenteritis have only mild symptoms, and the condition improves within a few days without the need for treatment.  However in certain cases, for example; if the symptoms are severe, persistent or recurrent and if the patient is especially vulnerable due to age or immune status, or in outbreaks of diarrhoea it may be clinically useful to isolate the causative agent

What type of viral investigations are carried out routinely?

The microbiology department only carries out in-house testing for rotavirus in paediatric patients (<5 years).  Norovirus testing is also carried out in outbreaks of diarrhoea and vomiting after notification by the Infection control team only.

How do I go about requesting virology investigations on individual patients that are not under 5 or part of an outbreak of diarrhoea and vomiting?

Any requests for testing of patient samples, which do not meet the above criteria, must be approved by a consultant microbiologist.  This can be done by contacting the on-call Consultant microbiologist through switchboard 01332 340171.  Please have the patient’s details ready.  Any samples submitted for virology thereafter must state on the request form that testing has been approved by a consultant microbiologist.  

What happens if I don’t get approval from a consultant microbiologist?

Please note that samples will not be examined for enteric viruses unless approved by a consultant microbiologist.  The microbiology department deals with a large volume of samples and aside from Rotavirus, samples have to be referred for viral investigation.

 

 

(Last modified by: AOM)

 

Last modified: 30/09/2015