Pertussis is a dangerous infectious disease that is well controlled world-wide by widespread immunization. The major cause of the decline in the morbidity and mortality of the disease is the intensive World Health Organization's Expanded Program on Immunization. However, pertussis still remains one of major diseases because of its high morbidity; an estimated 40 million pertussis cases occurred worldwide in 1994, resulting in 5 million episodes of pneumonia, 360000 deaths, and 50000 neurological complications (including permanent brain damage).