Whooping cough, medically known as pertussis, is a highly contagious bacterial infection that affects the airways. It gets its common name from the “whoop” sound that some infected children make when they take a deep, gasping breath after a severe coughing fit.

The infection is caused by the bacterium bordetella pertussis, with research suggesting that as few as 140 bacterial cells may be enough to cause infection. The bacterium spreads through infected droplets, which are released when an infected person coughs or sneezes. These droplets can then settle on the lining of another person’s nose, throat or airways.

Doctors usually describe whooping cough in three stages. The first is the catarrhal phase, when symptoms resemble a cold. In this stage, many of the symptoms are similar to other respiratory infections. A person may have a stuffy or runny nose, a low-grade fever and a mild, occasional cough that gradually becomes more severe. This phase typically lasts one to two weeks.

The second stage is the paroxysmal (sudden and intense) phase. During this stage, people experience repeated bouts of uncontrolled coughing. The classic whooping sound is common in infants, but it is often absent in adults. This may be partly because adults have more control over their cough reflex and partly because a child’s larynx, or voice box, is shaped differently from an adult’s. A child’s larynx sits higher in the neck, is funnel-shaped rather than cylindrical and narrower, and has softer cartilage.

The cough can last so long that pertussis is sometimes called the........

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