Whooping cough outbreaks: Why is pertussis on the rise in several countries?

Cases of whooping cough, or pertussis, have been on the rise in various countries, including the U.K., Australia and China. The U.S. has not seen similar upticks yet, although a few isolated outbreaks have been reported in 2024, as can be expected each year.

Here's what you should know about whooping cough and how to prevent the disease.

Related: Why do coughs linger after a cold?

What is whooping cough?

Whooping cough, also called pertussis, is an infection caused by the bacterium Bordetella pertussis, according to the Centers for Disease Control and Prevention (CDC). The disease gets its name from the characteristic, high-pitched "whoop" sound people with the illness often make when they inhale in the midst of a coughing fit.

B. pertussis invades the airways, latching onto small, hairlike extensions on the surfaces of cells and releasing toxins. According to the medical resource StatPearls, the word "pertussis" derives from the Latin words for "intense cough," and it's also known as the "the cough of 100 days."  

Pertussis spreads very easily between people. A measure of the disease's contagiousness, called its basic reproduction number (R0), is comparable to that of measles — the R0 of pertussis is estimated to be 12 to 17, while the R0 of measles is 12 to 18. The R0 reflects the number of susceptible people that one person infected with a disease would be expected to spread the illness to.

The infection can spread when ann infected person's coughs or sneezes, spewing bacteria into the air. It's thought that people are contagious from the start of their symptoms and for at least two weeks after they begin to cough. However, people with mild symptoms may not realize they have whooping cough and thus may unwittingly spread it to others.