Objectives: Aetiological diagnosis of parasitic infection of the intestinal tract by microscopic examination of stool specimens and identification of the parasite(s).

Test material: Faeces.

Equipment: Specimen container: a clean glass cup, a plastic or waxed cardboard box, or a special container with a spoon attached to stopper or lid. The use of penicillin bottles, match boxes and banana leaves should be discouraged, as they expose the nursing and laboratory staff to risk of infection.

Procedure: Direct smear and concentration method

1. Faecal material should be delivered in a clean bedpan, or on a paper towel or a piece of toilet tissue.

2. It should then be transferred to a suitable container provided with a lid. The specimen should contain at least 5 g and, if present, those parts that contain blood and/or mucopus should be selected. The specimen should not be contaminated with urine or contain barium, bismuth or oil.

Trophozoites of Entamoeba histolytica

1. The specimen should be kept warm and examined within 1 hour after defecation without previous refrigeration.

2. It is generally recommended that the examination be performed immediately and on the spot. A wet mount in saline of the mucopus from liquid or bloody stool is prepared and examined immediately under the microscope.

Storage: Refrigeration is generally not recommended; instead the stool specimen can be preserved for several weeks by mixing the specimen with at least 3 volumes of preservative fluid. A 10% formalin (3,4% formaldehyde) solution is recommended and is prepared by diluting 50 mL of commercial formalin (34%) with 450 mL of distilled water.

Transportation: Formed stool specimen may be sent by normal shipment. Liquid specimens or specimens with mucopus and blood should reach the laboratory within one hour and protected from cooling during transport. In a cold climate the specimen should either be collected at the laboratory itself or sent in a thermos bottle.

Reporting: The results will usually be sent out within 24 hours of receipt of the specimen.

Comments: No technique claims to be 100 per cent successful for the detection of parasites by a single stool examination. Cysts of Giardia lamblia and Entamoeba histolytica and larvae of Strongyloides stercoralis tend to be excreted in "showers" and it is generally accepted that five serial stools must be examined before an individual is considered free from these infections. For helminths more than one specimen is seldom necessary for a correct diagnosis. For the diagnosis of pinworm (Enterobius vermicularis) infection, the cellophane tape method is recommended.

Formed stools are examined microscopically after concentration for cysts, ova and larvae.

Loose stools without blood or mucopus are examined microscopically in saline for trophozoites of protozoa and after concentration for cysts, ova and larva.

Loose stools with blood and mucopus are examined microscopically in saline for trophozoites of Entamoeba histolytica, Balantidium coli, but not for cysts. Ova of Schistosoma mansoni or S. japonicum may be found.

Taenia segments and adult pinworm, if present, are also reported.

Special staining methods are needed (modified acid-fast stain, safranin-methylene blue) for the detection of oocysts of Cryptosperidium and Isospera.