Pertussis is spread by coughing. Whooping cough is highly contagious. When whooping cough spreads, symptoms will usually begin to occur 7 to 10 days after a person has been infected.
The greatest risk of spread is during the early
stage when it appears to be a cold, which makes it dangerous.
Even when treated with antibiotics, people are still contagious until
the first 5 days of appropriate antibiotic treatment have been completed,
which makes it dangerous to surrounding people.