Humans are the only known host for B. pertussis. Transmission occurs via direct contact with aerosolized droplets from infected individuals. Pertussis continues to be an endemic disease of worldwide importance with more than 195,000 deaths attributed to the disease each year.
In the United States, reports of B. pertussis infection declined dramatically following the introduction of pertussis vaccine, as shown in the image on the right. Case counts frequently exceeded 100,000 cases per year in the 1940s. By 1965 fewer than 10,000 cases were reported. During the 1980s pertussis reports began increasing gradually, and by 2012 more than 48,000 cases were reported nationwide, the most since 1955.* Although reported cases have decreased since the 2012 peak, the number of cases/year is still well above 10,000.
Studies have shown that the protection induced after natural infection or vaccination wanes after several years, leaving those individuals susceptible. For this reason, most cases of pertussis are generally seen in neonates, nonvaccinated young infants, older school-aged children, and adults.