Diagnosis of Giardia duodenalis infection in Bangladeshi infants: faecal antigen capture ELISA.

An enzyme-linked immunosorbent assay (ELISA) to detect antigens of Giardia duodenalis in faeces was evaluated as a diagnostic tool by testing faecal samples collected during a cohort study of 229 infants living in an urban slum in Dhaka, Bangladesh. Faecal samples had been collected at enrollment, on a routine monthly basis, and repeatedly during episodes of diarrhoea and infection with Giardia, and a portion of all samples was frozen in saline. A direct smear of all had been examined by microscopy and again after concentrating cysts by ether sedimentation. A total of 2121 of the 4936 samples stored during the 22 months study were tested by the ELISA. After excluding non-specific binding, the sensitivity of the assay was 94.2% and the specificity was 98%. The presence of other parasites, including flagellated protozoa, was not linked to false positive ELISA results. There was a correlation between the number of Giardia cysts present and the ELISA optical density. Assuming that the ELISA is 100% sensitive, microscopy detected 92.4% of the infections detected by the ELISA.