Pertussis is an acute bacterial, highly contagious, respiratory infection with a significant morbidity and mortality, especially in infants.1 In the United States, prior to the advent of vaccines, pertussis was the number one cause of pediatric (age <14 years) deaths from a communicable disease, accounting for 10,000 deaths annually and was responsible for more deaths in the first year of life than measles, meningitis, scarlet fever, diphtheria, and poliomyelitis combined.2 With the widespread use of the pertussis vaccine, there was a precipitous drop (>99%) in the number of cases of pertussis, reaching a nadir in 1976, with an increase in the incidence since then with epidemic pertussis occurring every 2 to 5 years since 1989.1
It is estimated that there are about 50 to 60 million cases with 300,000 to >500,000 deaths annually attributable to pertussis.1,3,4 There is a high incidence of pertussis in developing countries and nations with low vaccination rates. In the United States and Europe, in spite of widespread vaccination, the incidence of pertussis has been increasing.2–6 Considering just adolescents and adults, the number of pertussis cases per year in the United States is calculated to be around 600,000.1
In the United States, substantial epidemics occur every few years (e.g., in 2005, 2010, and 2012), with 2012 possibly the largest outbreak in 50 to 60 years.7,8 The resurgence of this vaccine-preventable disease has been attributed to several factors: (1) increased awareness of the disease, (2) availability of better laboratory tests for detection of Bordetella pertussis, (3) genetically modified changes in B. pertussis, (4) vaccine failures secondary to decreased potency of the vaccines, and (5) unimmunized individuals for religious or other reasons.
After immunization, there is a decline in antibody titers over time.5,7–9,11 Immunity begins to drop off during the third to fifth year after vaccination and is essentially nonexistent after 12 years.1,12–14 It is important to note that neither infection with pertussis (natural disease) nor vaccination provides lifelong or complete immunity against future reinfection or disease due to B. pertussis. The whole-cell vaccine, DTP vaccine, is more potent than the acellular vaccines, DTaP and Tdap vaccines, but has more side effects so the acellular vaccines are currently used (exclusively used since 1997) in the United States for immunization.10