Context Reported cases of pertussis among adolescents and adults have increased
since the 1980s, despite increasingly high rates of vaccination among infants
and children. However, severe pertussis morbidity and mortality occur primarily
Objective To describe the trends and characteristics of reported cases of pertussis
among infants younger than 12 months in the United States from 1980 to 1999.
Design, Setting, and Participants Cases of pertussis in infants younger than 12 months in the United States
reported to the National Notifiable Disease Surveillance System of the Centers
for Disease Control and Prevention between 1980 and 1999, and detailed case
data from the Supplementary Pertussis Surveillance System.
Main Outcome Measures Incidence and demographic and clinical characteristics of cases.
Results The incidence of reported cases of pertussis among infants increased
49% in the 1990s compared with the incidence in the 1980s (19 798 vs
12 550 cases reported; 51.1 cases vs 34.2 cases per 100 000 infant
population, respectively). Increases in the incidence of cases and the number
of deaths among infants during the 1990s primarily were among those aged 4
months or younger, contrasting with a stable incidence of cases among infants
aged 5 months or older. The proportion of cases confirmed by bacterial culture
was higher in the 1990s than in the 1980s (50% and 33%, respectively); the
proportion of hospitalized cases was unchanged (67% vs 68%, respectively).
Receipt of fewer doses of vaccine was associated with hospitalization, when
cases were stratified by age in months.
Conclusions The incidence of reported cases of pertussis among infants increased
in the 1990s compared with the 1980s. The limited age group affected, the
increased rate of bacteriologic confirmation, and the unchanged severity of
illness suggest that an increase in infant pertussis has occurred apart from
any change in reporting. Strategies are needed to prevent the morbidity and
mortality from pertussis among infants too young to be fully vaccinated, according
to the current recommended schedules of vaccination in the United States.