Pertussis was first recognized as an epidemic disease in the 16th century. The classic illness is a three-stage illness (catarrhal, spasmodic, and convalescent), with a distinctive cough, and its characteristics today are similar to those in the prevaccine era. In the prevaccine era, the calculated attack rate was 872/100,000 population, and the majority of cases occurred in children <5 years of age. On average, there were 7,300 deaths/year; the death rate began to decline before antimicrobial therapy and vaccination. Reported pertussis in adults was rare, but numerous investigators noted that atypical cases of pertussis were common in adults.