Whooping cough is a highly contagious respiratory infection caused by the bacteria Bordetella pertussis, which attaches to the lining of the upper respiratory system (sinuses, nose, and throat). The infection is primarily transmitted through person to person contact by breathing in or swallowing infected respiratory secretions that contain the bacteria. The bacteria may also be transmitted at a lesser rate through hand and surface contact with secretions. Once infected, the bacteria attach to the small hair-like extensions (cilia) of the upper respiratory tract and produce a toxin that damages the cilia and causes swelling.
Outbreaks of pertussis were first identified in the 16th century. The bacteria causing pertussis was formally isolated and identified in 1906. Once a common childhood disease, the invention of vaccinations to prevent pertussis infections has dramatically reduced the societal impact. However the WHO estimates that there are still 16 million cases of pertussis each year resulting in 200,000 deaths, primarily in developing countries where children are not immunized.
Infants are at the greatest risk of getting pertussis and once infected about half require hospitalization. Of those infants hospitalized, 1-2% die from the infection. Many infants that become infected with pertussis are infected by parents, older siblings, or caregivers that may not even know they are carrying the bacteria. Pertussis occurs worldwide but appears to be only a human disease. There are no known animal or insect sources.