Epidemiology

Humans are the only host of Bordetella pertussis. It is highly contagious, with rates of transmission of up to 80% among susceptible close contacts.[2]​ Prior to the advent of an effective vaccine in the 1940s, pertussis was one of the most common childhood infections, occurring predominantly in the summer and autumn, and in epidemics every 2-5 years. With the introduction of whole-cell pertussis vaccine in the US, reported cases of pertussis fell from 150 per 100,000 people to 1 per 100,000 people in the 1980s.[2]​​[4][5]​ Beginning in the 1990s, and coincident with a switch from whole-cell to acellular pertussis vaccines that was prompted by adverse events associated with whole-cell vaccine, the incidence of pertussis has increased, particularly in adolescents and adults. This increase is not completely understood. Contributing factors may include the more rapid waning of immunity following immunization with acellular pertussis vaccines, decreasing vaccination rates, changes in the pathogenicity of circulating strains of B pertussis, a greater awareness of the disease, and the increasing use of more sensitive nucleic acid amplification-based diagnostic tests.[4][6][7]

It is likely that large numbers of pertussis cases are not diagnosed and the true public health burden of the disease, therefore, is underestimated. Pertussis is endemic worldwide.[3]​ Globally, it continues to be a major cause of morbidity and mortality, especially in underimmunized populations.[4] Models suggest that in 2014 there were 24.1 million global cases of pertussis and 160,700 deaths in children ages <5 years, with the highest proportion of infections and deaths in the WHO African region.[8]

In the US, a decrease in pertussis incidence in infants ages <2 months has been observed following the introduction of the maternal tetanus-diphtheria-acellular pertussis (Tdap) vaccine, suggesting that maternal Tdap vaccination may be associated with a reduction in pertussis burden in this age group.[9]

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