Population-based incidence of pertussis among adolescents and adults, Minnesota, 1995-1996

To estimate the incidence of pertussis, a prospective study was done among members of a managed care organization in Minneapolis/St. Paul, Minnesota. Of 212 patients 10-49 years old enrolled from January 1995 through December 1996, 8 were found to be culture positive, 10 were found to be positive by polymerase chain reaction assay, 13 had a greater than or equal to2-fold i ncrease in IgG or IgA to pertussis toxin (PT), and 18 had IgG to PT in a si ngle serum specimen greater than or equal to3 SD above the mean of an age-m atched control group. At least 1 positive laboratory test result for pertus sis infection was found in 27 (13%) patients, among whom the duration of co ugh illness was a median of 42 days (range, 27-66 days). On the basis of an y positive laboratory result, the estimated annual incidence of pertussis w as 507 cases per 100,000 person-years (95% confidence interval, 307-706 cas es). Bordetella pertussis infection may be a more common cause of cough ill ness among adolescents and adults than was recognized previously.