Age-related differences in patterns of increased Bordetella pertussis antibodies

During the period 2008 to 2010, we identified 11,386 serum samples with increased (positive) levels of antibodies recognizing Bordetella pertussis antigens. We sought to characterize the distribution of positive antibody result patterns in relation to patient age. IgG and IgA antibodies recognizing pertussis toxin (PT) and filamentous hemagglutinin (FHA) were quantified using a multianalyte immunodetection assay. Four mutually exclusive positive result patterns were observed: increased FHA antibodies only, increased PT IgA but not IgG, increased PT IgG but not IgA, and increased PT IgG and IgA. In patients < 21 years old, the predominant pattern was increased PT IgG but not IgA, whereas in patients ≥ 21 years old, it was increased FHA antibodies only. The proportion of positive serum samples exhibiting increased PT IgA but not IgG was < 20% in all age categories but showed a stepwise rise with age. The proportions of positive serum samples exhibiting increased PT IgG and IgA were similar (26 to 32%) in the age categories spanning 11 to 60 years of age but lower in the < 11- and > 60-year-old groups. In 3 of 5 age categories, a significant rise in the proportion of positive serum samples exhibiting increased FHA antibodies only occurred in 2010. Patterns of positive B. pertussis antibody results varied with age. The predominance of increased FHA antibodies only in patients > 20 years old suggests that many adults thought to have B. pertussis infections actually have other infections that induce FHA-reactive antibodies. Similarly, the 2010 rise in the frequency of increased FHA antibodies only in some age groups suggests an increase in non-B. pertussis infections.