Specificity and sensitivity of high levels of immunoglobulin G antibodies against pertussis toxin in a single serum sample for diagnosis of infectionwith Bordetella pertussis

Laboratory confirmation Of pertussis qv culture, PCR, or detection of antib ody increase in paired sera is hampered by ion sensitivity in the later sta ges of the disease. Therefore? we investigated whether, and at which level, concentrations of immunoglobulin G (IgG) antibodies against pertussis toxi n (PT), IgG-PT, in a single serum sample are indicative of active or recent pertussis, IgG-PT, measured by enzyme-linked immunosorbent assay in units per milliliter, was analyzed in 7,756 sera collected in a population-based study in The Netherlands, in the sera of 3,491 patients with at least a fou rfold increase of IgG-PT in paired sera of 89 patients with positive cultur es and/or PCR results, and in the sera of 57 patients with clinically docum ented pertussis with a median follow-up of 1.4 years. We conclude that? ind ependently of age, IgG-PT levels of at least 100 U/ml are diagnostic of rec ent or active infection with Bordetella pertussis. Such levels are present In less than 1% of the population and are reached in most pertussis patient s within 4 weeks after disease onset and persist only temporarily.