Microbiology

Faecal Specimens

Specimens of faeces are required for the identification of enteric pathogens. The specimen may be passed into a clean, dry, bedpan or similar container and transferred to a blue poly pot (with spoon) specimen container. The specimen is unsatisfactory if there remains any residual soap, detergent or disinfectant in the pan.

If bacterial gastroenteritis is suspected, a minimum of 2 specimens should be taken at least 24 hours apart and the date and time of collection clearly stated. Multiple specimens that do not have a date or time or are taken on the same day will be treated as a single specimen. No more than 3 specimens should be sent in any episode of diarrhoeal illness.

Faecal samples from patients with acute diarrhoea are routinely examined for Cryptosporidia, Shigella, Salmonella, Campylobacter and E. coli 0157. Additional tests e.g. parasites; Yersinia spp. will be done according to clinical details. Depending on the age of the patient and clinical circumstances examination for rotavirus or norovirus may be carried out.

Always give full clinical details including date of onset, presence of blood and state if the patient has been abroad or is on antimicrobial therapy, since this may be indicative of antibiotic-induced diarrhoea. The range of tests performed on a sample is determined by the clinical information provided.

Isolation of enteric pathogens that may be part of an outbreak or a cause of suspected food poisoning are reported to the Humber Health Protection Unit. These patients should expect to be contacted by an Environmental Health Officer who will investigate the source of infection and give advice on preventing further spread of infection.

Follow up specimens from symptomless patients with previously identified enteric pathogens are not required unless requested by the Health Protection Unit. Follow up (clearance) specimens requested by commercial food manufacturers or caterers on their employees are category 2 specimens and a charge will be levied.

Faeces for Clostridium difficile testing

If clinically indicated, patients who fulfil any of the following criteria should be screened: antibiotic-associated diarrhoea (everyone over the age of two); pseudomembraneous colitis; all patients over 65 years old with diarrhoea. In addition, all inpatient and hospital associated (outpatient clinic) faeces samples fulfilling the Bristol stool chart requirements 5-7.

Faeces for Faecal parasitology

Faecal samples from patients with chronic diarrhoea (diarrhoea for >1 week) are also examined for parasites. Ideally three faecal samples should be collected over no more than a 10-day period. It is recommended that specimens be collected every other day, as shedding of cysts and ova tends to be intermittent. Please state if the patient has travelled abroad. For the diagnosis of amoebic dysentery or amoebic abscess, please contact a Consultant Microbiologist.

Threadworm ova are not usually found in faeces. Please send a plain dry sterile swab (not charcoal) that has been rolled around the perianal surface.

Faeces for Helicobacter pylori (H pylori)

This is a test for the presence of H pylori antigen in the faeces. It is sensitive and specific but false negative results can occur if the test is performed within 4 weeks of the end of antibiotic or bismuth therapy. The result should be interpreted in conjunction with other clinical findings and/or diagnostic procedures. A positive test result alone is not an indication for eradication therapy. Specimens over 2 days old on receipt are unsuitable for examination and will be considered unsuitable for examination if date and time of collection not stated.