Evaluation of a tetraplex microsphere assay for Bordetella pertussis antibodies

To increase testing efficiency, a microsphere-based multianalyte immune detection (MAID) system was developed to measure serum immunoglobulin G (IgG) and IgA recognizing two Bordetella pertussis antigens, pertussis toxin (PT) and filamentous hemagglutinin antigen (FHA). The assay was performed as two separate duplexes. One duplex measured IgG to PT and FHA, and the other measured IgA to PT and FHA. The two duplexes were then combined and analyzed as a tetraplex. The MAID system and an in-house enzyme-linked immunosorbent assay (ELISA) system were used to evaluate 100 sera from blood donors and 220 consecutive sera submitted for B. pertussis antibody testing. For both the MAID and ELISA systems, antibody levels were defined as increased if greater than the blood donor group 95th percentile value. The qualitative concordance rates between MAID and ELISA results for the 220 consecutively submitted sera were as follows: PT IgG, 99%; PT IgA, 94%; FHA IgG, 93%; FHA IgA, 94%. The overall concordance rate was 95% (836 of 880 result sets). For 29 of 44 (66%) discordant result sets, the discordant MAID result was supported by the MAID and ELISA results for other B. pertussis antibodies. The MAID and in-house ELISA systems were also used to evaluate 20 sera previously tested for pertussis antibodies at a pertussis vaccine research laboratory; MAID results for all four analytes did not significantly differ from results obtained by the research laboratory. These findings show that antibodies to B. pertussis antigens can be measured easily and accurately using a tetraplex microsphere system.