Whooping cough is a respiratory infection caused by a gram-negative bacterium called Bordetella pertussis. Pertussis is endemic to the United States, with epidemics occurring every 3-5 years and with an average 5000-7000 cases per year. However, since the 1980s, the incidence of whooping cough has increased, with more than 10,450 cases reported in 2007. The last major outbreak occurred in 2005, with more than 25,000 cases. Health officials are hoping to prevent another such outbreak.
Since the 1990s, cases have disproportionately increased in older children and young adults, likely because of anti-vaccine momentum among their parents and possibly evolution of the bacterium itself. Read more about why cases of whooping cough are increasing.