Epidemic pertussis in 2012--the resurgence of a vaccine-preventable disease.

n engl j med 367;9 nejm.org august 30, 2012 785 in 50 years. Why has this theoretically vaccine-preventable disease been on the upswing? The past 45 years have seen concern about the safety of the diphtheria–tetanus–pertussis (DTP) vaccine, epidemics stemming from the vaccine’s decreased use, and the development of new vaccines using acellular pertussis components (DTaP). In the prevaccine era, the number of reported cases of pertussis reached epidemic proportions every 2 to 5 years.1,2 Pertussis immunization in the United States reduced the average incidence from 157 per 100,000 population in the early 1940s to less than 1 per 100,000 in 1973. Nevertheless, the cycles of outbreaks continued to occur, because neither infection nor immunization produces lifelong immunity to pertussis, as they do for diseases such as measles; as measles was being brought under control, the period between epidemics lengthened, and there was less clinical disease and less circulation of the virus. Since cycles of pertussis continue to occur today, we know that Bordetella pertussis is continuing to circulate in a manner similar to that of the prevaccine era. Around 1982, the incidence of pertussis started to gradually increase; in 2005 and 2010, substantial epidemics occurred, and another epidemic is now under way (see graph).1-5 There are actually two relevant epidemiologies to consider: the epidemiology of reported pertussis cases and the epidemiology of B. pertussis infection.2 The former depends on the surveillance program we have in place: the more complete it is, the higher the reported incidence will be. As for the latter, over the past 25 years, three types of studies have been performed to gain insight into B. pertussis infection.1,2 The first type examined the cause of prolonged illnesses involving cough in adolescents and adults; the findings suggested that 13 to 20% of these cough illnesses were attributable to B. pertussis infection. In the second type of study, a parEpidemic Pertussis in 2012 — The Resurgence of a Vaccine-Preventable Disease