How could whooping cough (pertussis) spread to my child?

Pertussis is very contagious (spreads easily from one person to another). It spreads through the air in droplets when an infected person coughs or sneezes. These droplets can also get on people’s hands. Washing your hands is one of the easiest ways to help prevent the spread of pertussis. The incubation period is usually 7 – 10 days, but could be as long as 21 days.