Evaluation of a single-sample serological technique for diagnosing pertussis in unvaccinated children

This study was performed to evaluate the sensitivity of immunoglobulin (Ig) G and IgA antibodies to pertussis toxin and filamentous hemagglutinin in di agnosing pertussis from a single serum sample. The pertussis group was defi ned according to the World Health Organization pertussis case definition. T he control group coughed for 21 days or more but had no microbiological or serological evidence of Bordetella infection. Both cohorts were divided int o infants (<12 months of age), toddlers (1-4 years) and school children (5- 10 years). There were 525 subjects in the pertussis group and 321 in the co ntrol group, with an even distribution of genders. IgG and IgA antibodies t o pertussis toxin and filamentous hemagglutinin were measured in a standard ized enzyme immunoassay. Antibody levels beyond the 95 percentile of the co ntrol cohort were regarded as indicative of recent contact, setting the spe cificity level at 0.95. Acute serum samples drawn between 1 week and 3 week s after the onset of coughing showed a low sensitivity (2-19%) for diagnosi ng pertussis. In convalescent samples taken 5-10 weeks after the onset of s ymptoms, detection of IgG anti-pertussis toxin was the best single test, wi th a sensitivity of 61%, 65%, and 74% in infants, toddlers and school child ren, respectively. A combination of IgG anti-pertussis toxin and IgA anti-f ilamentous hemagglutinin using age-specific reference values had a sensitiv ity of 81-89% in diagnosing pertussis from a single serum sample taken 5-10 weeks after the beginning of symptoms.