Whooping cough: what it is, who’s most at risk, how to prevent it and why it’s nicknamed the 100-day cough

Whooping cough is caused by the bacteria Bordetella pertussis, which is transmitted through respiratory droplets when an infected person coughs or sneezes.

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The bacteria attach to the cilia – tiny hairlike extensions – that line part of the upper respiratory system, where they release toxins that damage the cilia and cause airways to swell, says Dr Andrew Kong, a general practitioner in private practice in Hong Kong.

The illness is hard to definitively diagnose, says Dr Sarah Borwein, also a general practitioner in private practice in Hong Kong.

“You can use PCR [polymerase chain reaction] testing of a nasopharyngeal specimen, like with the early Covid tests, but only during the first four weeks of infection, and in practice, doctors rarely consider the diagnosis of whooping cough until the cough has gone on longer than that,” Borwein says.

“After that, you have to rely on serology [antibody testing], which has relatively low sensitivity and can be complicated by antibodies from previous vaccination.”

Whooping cough is associated with a number of symptoms, many of which are flu-like.

“It is an intense cough that may last for up to 12 weeks, and between bouts of coughing you can be perfectly well,” says Dr Lily Wong, a general practitioner in Hong Kong. “This is different from most normal coughs, which clear up within three weeks.

“There is a high-pitched ‘whoop’ sound when you’re finally able to inhale at the end of a coughing fit. This is the main difference between whooping cough and a regular cough.

“You may also experience a runny nose, fever, vomiting and exhaustion after a coughing fit.”

Borwein says that whooping cough is persistent and resistant to treatment, and is sometimes called the “100-day cough” because no matter what you do, it can last more than three months.

Whooping cough in young infants can also cause life-threatening pauses in breathing (apnoea spells), seizures and brain damage.

“About one-third of infants younger than one year old with whooping cough need hospital care to clear their airways of mucus using suction. They may also need oxygen support,” says Wong.

“Watch out for complications such as pneumonia, which can be more severe, and ensure that an ill child is adequately nourished and hydrated,” she adds, stressing that the most effective way to prevent whooping cough is through vaccination.

Wong adds that elderly patients have the second-highest hospitalisation rate from whooping cough, probably due to fading immunity.

“Whooping cough can cause complications in adolescents and healthy adults too, but is far less serious, especially in those who have been vaccinated,” Borwein says.

“Complications can include broken ribs from coughing, loss of bladder control and fainting.”

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There is an effective vaccine for whooping cough. In adults, it is about 80 per cent effective at preventing whooping cough; however, this wanes relatively quickly and is probably only about 50 per cent effective five years after vaccination, Borwein says.

Infants are given the pertussis vaccine as part of their routine immunisation programme. They need three doses, however, and are not well protected until six months of age, Borwein says. This leaves them poorly protected at the time they are most vulnerable to severe complications.

“For this reason, the vaccine is now administered routinely to pregnant women in every pregnancy. This has been shown to give passive immunity to their babies in the first few months of life and has been a major advance in reducing the toll of whooping cough in infants,” she adds.

In adolescents and adults, the vaccine is included as part of a tetanus-diphtheria vaccine (Tdap, or tetanus-diphtheria-pertussis vaccine). The recommendation is to have one dose every 10 years.

According to Borwein, some experts think this period should be shortened because efficacy wanes significantly after about five years. Even after natural infection, immunity wanes over the years and there is a possibility of reinfection.

The bacteria that cause whooping cough can be eliminated with antibiotics that are typically prescribed if the diagnosis is made within the first three weeks of the illness.

Specific antibiotics, such as azithromycin, can reduce the likelihood of infected individuals transmitting the illness to others – but they do not alleviate symptoms.

Unfortunately, there are limited effective medicines to control the cough itself, although some medications can alleviate fever and runny nose.

There is no quick fix for the coughing fits; Kong says to be patient as the symptoms tend to resolve with time.

Avoid exposure to other respiratory infections, get plenty of rest, stay hydrated, and avoid contact with irritants like smoke, dust and chemical fumes, he says.

A cool-mist humidifier may help to loosen mucus and soothe the cough.

“Most people try all kinds of things, including cough medicines and inhalers, but no medications have been shown to help significantly,” Borwein says.

“You’re best advised to stay up to date with vaccination to prevent or mitigate whooping cough in the first place.”