Faeces - microscopy, culture and antigen detection

Last updated: Sunday, 21, May, 2006

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Item Process
Specimen

Fresh stool, delivered as soon as possible to the laboratory. The specimen should be refrigerated only if a delay of >6 hours is likely.

Rectal swabs are not suitable except for screening for cancomycin-resistant enterococci (VRE).

Full clinical information should be provided on the request form, especially the presence and duration of symptoms, recent travel or shellfish ingestion, previous antibiotics and purpose of culture (that is, whether the culture is for diagnosis in a patient with diarrhoea, detection of a carrier state or to document clearance of a specific organism).

If required, examination for ova, cysts and parasites should be specifically requested: see Faeces - ova, cysts and parasites.

Testing for Clostridium difficile toxin and viral detection must also be specifically requested if required.

Method

Microscopy of wet film.

Culture on selective media for Salmonella, Shigella and Campylobacter sp, and (if clinically appropriate) for Aeromonas hydrophila, Yersinia spp, Vibrio parahaemolyticus, Vibrio cholerae and Shiga toxin-producing Escherichia coli.

Molecular genetics using PCR probes may be used to detect Shiga toxin-producing E. coli.

Testing for Clostridium difficile toxin is required in antibiotic-associated diarrhoea; some laboratories also culture for Clostridium difficile.

In children, EIA for detection of rotavirus and adenovirus antigen.

PCR or electron microscopy for norovirus, and the like, in the investigation of diarrhoeal outbreaks.

Viral culture, detection in the investigation of meningitis and encephalitis.

Application

Diarrhoea, when severe or prolonged;
enteric fever or typhoid carrier state;
haemolytic uraemic syndrome (Shiga toxin-producing E. coli);
PUO;
aetiological diagnosis during outbreaks of viral meningitis or encephalitis.

Interpretation

The presence of white cells or red cells is significant.

Isolation of a recognised pathogen does not exclude the possibility of underlying inflammatory bowel disease (eg, Crohn’s disease, ulcerative colitis).

The significance of a bacterial isolate depends on clinical circumstances.

See also Faeces - ova, cysts and parasites and Clostridium difficile toxin.

Reference

Hines J and Nachamkin I. Clin Infect Dis 1996; 23: 1292-1301.

Thielman NM and Guerrant RL. N Engl J Med 2004; 350: 38-47.