The disease still carries significant morbidity and mortality in infants less than 2 years of age. Pertussis should be included in the differential diagnosis of protracted cough with cyanosis or vomiting, persistent rhinorrhea, and marked lymphocytosis. A mucopurulosanguinous exudate is formed in the respiratory tract.
Most cases occur in the late summer and early fall.
This decreased to a low in 1976, when there were 1,010 cases with only 4 deaths. Pertussis is the most commonly reported vaccine-preventable disease among children in the U.S. who are younger than 5 years of age. Germany had a similar occurrence in the 1980s and 90s. This approaches the pre-vaccination era incidence. Recent similar epidemic outbreaks have occurred in Sweden, Canada, and Germany.