Pertussis, also known as whooping cough, is a highly contagious isease caused by the bacterium Bordetella pertussis; it derived its name from the characteristic severe hacking cough followed by intake of breath that sounds like "whoop"; a similar, milder disease is caused by B. parapertussis. Although many medical sources describe the whoop as "high-pitched", this is generally the case with infected babies and children only, not adults.