It is caused by a bacterium.
People can get pertussis at any age and at any time of year.
It is very contagious and symptoms range from mild to severe. Pertussis often begins gradually with cold-like symptoms and an irritating cough. Severe coughing spells develop, followed by whoops which can lead to the ill person turning blue or having trouble catching his or her breath, and sometimes vomiting after coughing. The coughing spasms may occur several times a day and last from four to six weeks. These severe symptoms are most common in young children.