Pertussis, also known as whooping cough, is an acute bacterial (Bordatella pertussis) infection of the cilia that line the air passages of the lower respiratory tract. Cilia are tiny, hairlike projections on cells that beat back and forth to help clear the respiratory system of mucus, bacteria, viruses, and dead cells. Bordatella pertussis interferes with the motion of the cilia. The debris accumulates and causes irritation in the respiratory tract and triggers coughing. It causes spasms (paroxysms) of uncontrollable coughing, followed by a sharp, high-pitched intake of air which creates the characteristic whoop for which the dis¬ ease is named. Pertussis is very contagious and is spread by breathing in airborne droplets expelled from the nose or throat of an infected person or by direct contact with dis¬ charges from the nose or throat of an infected person.