Evaluation of specific serum anti-Giardia IgM antibody response in diagnosis of giardiasis in children.

Diagnosis of Giardia intestinalis infection is usually made by examination of stool specimens and/or by more invasive methods such as microscopy of duodenal juice or small bowel mucosal biopsies. Serological diagnostic methods have been developed but have not been evaluated in children. In this study specific anti-Giardia immunoglobulin (Ig) M, IgG and IgA antibody titres were measured by enzyme-linked immunosorbent assay. Giardia parasites were sought in jejunal mucosal biopsies and in faeces from 72 children in The Gambia, West Africa; 50 jejunal biopsies, 271 stool samples and 95 serum samples were examined for evidence of Giardia infection. As a diagnostic test, a raised specific anti-Giardia IgM antibody titre (greater than or equal to 1:800) had a sensitivity of 63% and specificity of 93%, with a positive predictive value of 85% and a negative predictive value of 81%. There was poor correlation between positive microscopical identification of Giardia and elevated specific anti-Giardia IgG or IgA antibody titres in children on admission to the study. Elevated serum anti-Giardia IgM, however, was correlated well with active Giardia infection and may prove useful in epidemiological studies of giardiasis in developing countries.