Our initial investigation revealed that two rapid antigen capture enzyme immunoassays (EIA) did not detect wild type avian influenza virus type H5N1 [A/Vietnam/1203/2004(H5N1)] at a concentration of 50,000 TCID50. We challenged the rapid EIAs with a 10 fold dilution series of wild type viruses from 10 to 1,000,000 TCID50 and found the EIAs could detect A/Vietnam/1203/2004(H5N1) and A/Indonesia/05/2005(H5N1) at 1,000,000 and 100,000 TCID50 respectively, but neither assay detected A/Hong Kong/491/1997(H5N1) at any dilution. These data suggest that these assays require high virus concentrations, such as those found in nasopharyngeal washes from symptomatic patients early in their infections, to detect avian influenza virus type H5N1.
