A new immune complex dot assay for detection of rotavirus antigen in faeces

A new immune complex dot assay (ICDA) using immune gold/silver staining is described for the sensitive and rapid detection of rotavirus in cell culture and stool specimens. The method involves spotting preformed antigen-antibody complexes onto nitrocellulose paper, followed by incubation with colloidal gold-labelled secondary antibody and silver enhancement. ICDA was sensitive and specific and detected rotavirus antigens over a wide range of concentrations. It was more sensitive than a conventional immunodot assay (CIDA) and two commercial enzyme immunoassays (EIA) based on testing serial dilutions of a positive stool specimen. Of 26 stool specimens tested ICDA detected rotavirus antigen in 17; 14 were positive by Pathfinder Rotavirus EIA, 16 by Testpack Rotavirus EIA, and direct electron microscopy (DEM) detected only 12. The ICDA offers improved sensitivity over commercial EIAs and DEM.