Transmission of pertussis from adult to infant--Michigan, 1993.

During 1993, a total of 6586 pertussis cases was reported in the United States, including 675 (10%) cases among persons aged > 19 years. However, the total number of cases probably was substantially higher because only an estimated 10% of all pertussis cases are reported (1); underreporting is greater among adults, who often have only a mild cough. This report summarizes the investigation of two cases of pertussis in which transmission occurred from an adult resident of Massachusetts who was visiting the residence of an infant in Michigan.