Immunodiagnostic detection of Giardia antigen in faeces by a rapid visual enzyme-linked immunosorbent assay.

An enzyme-linked immunosorbent assay (ELISA) was developed for the detection of Giardia antigen in human faeces. 136 faecal samples were tested; 76 were positive and 27 negative for giardia cysts on microscopy, and 33 samples contained a range of other parasites. The ELISA sensitivity exceeded 98% and its specificity was 100%, by both colorimetry and direct visual interpretation. The assay could trace the decline and disappearance of antigen in faeces rendered microscopically negative by chemotherapy. This ELISA, which can be completed in less than 3 h and which does not rely on complex equipment for interpretation, should be very useful in diagnostic and epidemiological applications.