Protective role of immunoglobulin G antibodies to filamentous hemagglutinin and pertactin of Bordetella pertussis in Bordetella parapertussis infection.

An outbreak of parapertussis was studied prospectively in 38 first and second grade pupils of an elementary school. Eleven (29%) children were confirmed to be culture positive for Bordetella parapertussis. Serum samples were collected from 31 children for assay of antibodies to filamentous hemagglutinin (FHA), pertactin (PRN), and pertussis toxin of Bordetella pertussis. At the first sampling, ten children were found to have a cough and 21 were asymptomatic. Of the latter, 12 remained asymptomatic and eight developed cough within 11 to 53 days (mean +/- standard deviation, 31 +/- 12 days) after sampling. One child was identified as culture positive for Bordetella pertussis and, thus, not included in the analysis of Bordetella parapertussis infection. The mean levels of IgC antibodies to FHA and PRN were significantly higher in the 12 asymptomatic children than in the eight children who later developed cough or in 20 healthy control children of the same age (for FHA, p = 0.009 and < 0.001, respectively; for PRN, p = 0.002 and 0.002, respectively). These preliminary data suggest that Bordetella parapertussis infection is more prevalent than documented, and that children with high levels of IgG antibodies to FHA and PRN can remain asymptomatic.