Whooping cough is a serious bacterial infection of the lungs and breathing tubes that causes violent coughing fits. The disease gets its name from the distinctive “whoop” sound people make when they gasp for air after coughing. During a coughing fit, a person might cough dozens of times in a row without being able to catch their breath, then make a high-pitched whooping noise as they finally inhale.

Before vaccines were developed in the 1940s, whooping cough killed thousands of children every year. The coughing fits can be so severe that they make people vomit, break ribs, or pass out from lack of oxygen. Babies are especially vulnerable because their airways are so small. The disease spreads easily when infected people cough or sneeze, sending tiny droplets containing the bacteria into the air.

The medical name for whooping cough is pertussis. While the vaccine has made the disease much less common, it still exists and can spread quickly in communities where people aren't vaccinated. The characteristic whooping sound comes from swelling and mucus in the airways, which makes it hard to breathe normally. A person with whooping cough might feel fine between coughing fits, but when the fits hit, they can last for weeks or even months, which is why doctors sometimes call it the “100-day cough.”