Frequency of unrecognized Bordetella pertussis infections in adults.

To investigate the frequency of unrecognized Bordetella pertussis infections in adults, we performed IgA and IgG ELISA antibody studies with four B. pertussis antigens--i.e., lymphocytosis-promoting factor, filamentous hemagglutinin, pertactin, and fimbriae-2--in 51 health care workers from whom six consecutive yearly serum samples (from 1984 to 1989) were available. Overall, 90% of the subjects had a significant increase in antibody (IgA or IgG) to one or more antigens between 2 consecutive years during the 5-year study period; 55% of subjects had evidence of two infections, 17% had three infections, and 4% had four infections. Infections occurred in all study years, with the following rates: 1984-1985, 32%; 1985-1986, 24%; 1986-1987, 40%; 1987-1988, 29%; and 1988-1989, 43% (P = .12). Some antibody rises may have been due to responses to cross-reacting antigens (Bordetella parapertussis, nontypable Haemophilus influenzae), but overall these data suggest that B. pertussis infections in adults are common, endemic, and usually unrecognized.