Causes of Whooping Cough
Whooping cough is primarily a disease of infants and preschool children. A child usually gets the infection from another who is infected with Pertussis. The bacilli occur abundantly in the naso–pharyngeal and bronchial secretions, which are infective. The organisms make their way into the atmosphere every time the patient coughs or sneezes. A susceptible child, particularly one who is not immunized can inhale these organisms. Close contact enhances the chances of getting the infection rather than remote contact. The organisms then multiply in the respiratory tract to cause the infection.

Environmental factors and the spread of Pertussis
Pertussis occurs throughout the year, but the disease shows a seasonal trend with more cases occurring during the winter and spring months, due to overcrowding. The risk of exposure is greater in the lower socio–economic class.

Immunization/infection and lifelong immunity
Recovery from whooping cough or adequate immunization is followed by immunity.

The incubation period of whooping cough is usually about 10 to 14 days.