Whooping cough is primarily a disease of infants and preschool children. A child usually gets the infection from another child who is infected with Pertussis. The bacilli occur abundantly in the naso-pharyngeal and bronchial secretions, which are infective. The organisms are 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 than remote contact.
The incubation period is usually 10-14 days. Environmental Factors and the spread of Pertussis Pertussis occurs throughout the year, but the disease shows a seasonal trend with more cases occurring during winter and spring months, due to overcrowding. The risk of exposure is greater in the lower socio economic class. Recovery from whooping cough or adequate immunization is followed by immunity. It multiplies on the surface epithelium of the respiratory tract and causes inflammation and necrosis of the mucosa.