October 2011, Volume 41 Number 10 , p 61 - 62
THE INCIDENCE OF pertussis, commonly known as whooping cough, has been on the rise during the last two decades, even in countries with high vaccination coverage.1 Although it's usually thought of as a pediatric infection, pertussis is highly contagious and also infects adolescents and adults.2 In 2009, almost 17,000 cases of pertussis were reported in the United States, but many more may be undiagnosed and not reported.3Pertussis, or "violent cough," was first described in 1540.2 The bacterium Bordetella pertussis is transmitted from person to person by large respiratory droplets during talking, coughing, and sneezing. Individuals with pertussis may be asymptomatic but still infectious. Others may develop a mild cough or paroxysmal coughing episodes. Pertussis transmission to exposed household contacts can be as high as 90%.2Adolescents and adults may become infected and transmit pertussis to susceptible infants in the home, daycare, healthcare settings, and the community. Older adults may also transmit the infection to infants; grandparents are increasingly providing childcare for working parents, and one study found that grandparents were responsible for 6% to 8% of pertussis transmission to infants.4 Infants under age 6 months have the highest infection rate and are at greatest risk for severe disease and death.5The increasing number of pertussis cases since the 1980s is due in part to waning immunity from previous pertussis infection or vaccination. Waning immunity occurs 4 to 20 years after natural infection and 4 to 12 years after vaccination.6 Additional reasons for the increase include bacterial genetic mutations, making the current pertussis vaccine less effective; a heightened awareness of the illness in certain age groups, leading to more cases being diagnosed and treated; and improved lab testing.2Initial signs and symptoms of pertussis in adults can mimic those of other respiratory diseases such as influenza, Mycoplasma pneumoniae, and Chlamydia pneumoniae.