Pertussis (Whooping Cough): On the Rise—Again

“Pertussis vaccine is a good vaccine, but if it’s not used, [disease] can spread like wildfire through a community.”

Robert W. Frenck, Jr., MD, pediatric infectious disease specialist, Cincinnati Children’s Hospital

“Acting is merely the art of keeping a large group of people from coughing.”

Sir Ralph Richardson, English actor

Tired of hearing about the barrage of viruses that attack the respiratory tract? This week’s post offers a reprieve. It’s about Bordetella pertussis, a bacterial pathogen that causes the notorious respiratory tract infection whooping cough (aka pertussis).

Whooping cough outbreaks are surging across the U.S, Europe, and Asia due to relaxation of measures that protect against SARS-CoV-2, the virus that causes COVID-19. In the first five months of 2024, the Centers for Disease Control and Prevention tracked about 5,000 cases of pertussis in the U.S.—more than double the number for the same period last year. Given the rise in cases, I thought it time to get this highly contagious infection back on our radar screens. (See December 23, 2019 Germ Gems “Pertussis [Whooping Cough]: Nothing To Sneeze At.”)

Pathogen and pathogenesis. Bordetella pertussis (B. pertussis), a small gram-negative coccobacillus, is the etiologic agent of whooping cough. In 1906, the Belgian bacteriologist Jules Bordet discovered that this bacterium infects the respiratory epithelium of mammals. (He was awarded the 1919 Nobel Prize in Physiology or Medicine for his work.) The bacterium was named after Bordet coupled with the word “pertussis” meaning intensive cough—a hallmark of the disease, whooping cough.

B. pertussis is primarily transmitted from person to person through aerosolized respiratory droplets generated by coughing or sneezing. Although direct contact with respiratory secretions is also a mode of transmission, it’s mainly the inhalation of “infectious respiratory particles” expelled by coughing, sneezing, talking, singing, or spitting that initiates pertussis. Pertussis inflames the bronchial tubes, or airways, making it difficult to breathe and can lead to pneumonia, the most common complication of pertussis.

Epidemiology. The mortality rate of whooping cough varies with age, vaccination status, and geographic region. Globally, pertussis kills approximately 300,000 people annually, with the majority of deaths occurring in developing countries.

As with many infectious diseases, the risk of dying from whooping cough is markedly skewed by age with most deaths occurring among infants who are too young to be fully vaccinated. In the U.S., the mortality rate among those younger than three months is 1-3%. (To date this year in the U.S., five infants have died from whooping cough.)

In the 1980s, cases of pertussis began to increase steadily worldwide. But beginning in early 2020, the rate of whooping cough cases, along with several other respiratory tract infections, declined significantly due to the protective measures used to ward off COVID-19, e.g., masking and social distancing.

During the early months of the pandemic, however, some children missed vaccination appointments leaving them vulnerable to B. pertussis. So, it’s not surprising that as protective measures loosened against respiratory tract infection by SARS-CoV-2, coupled with reduced childhood vaccinations, the rate of whooping cough cases took a U-turn and started increasing yet again.

Signs and symptoms. The first signs of whooping cough are similar to a cold, e.g., runny nose, sore throat, and a cough. After about a week, the infection develops into coughing bouts that last for a few minutes. Some, but not all, young babies may also make a distinctive “whoop,” or may have difficulty breathing after a bout of coughing, or  have incessant coughing (aka “cough seizures”),  or cough until they “turn blue.” But in most cases, the cough is just unusually prolonged—lasting up to three months. (In China, whooping cough is called the “100 day cough.”)

Pertussis is best known for its toll on babies. But the disease can also cause serious illness in people older than 65, who are prone to developing not only pneumonia but also rib fractures from violent coughing.

The diagnosis of whooping cough is usually guided by the clinical index of suspicion (including the characteristics of the cough and a history of exposure to someone with the illness) and is confirmed by culture or PCR test of a nasopharyngeal sample. 

Treatment. A physician familiar with the disease should guide the management of patients with whooping cough. As it is a bacterial infection, it is treated with an antibiotic, such as a macrolide (erythromycin, azithromycin, or clarithromycin) or trimethoprim-sulfamethoxazole. Treatment is most effective during the first 1–2 weeks of the illness, before coughing paroxysms occur. Early treatment can reduce the severity, duration, and risk of complications, especially in infants. It can also help prevent the spread of the disease to others.

Prevention. Vaccination is the cornerstone of prevention of whooping cough. The pertussis vaccine, which is included in the DTaP (diphtheria, tetanus, acellular pertussis) shot, is 98% protective within a year of children receiving the final dose of a five dose regimen (including a 3-dose series at age 2, 4, and 6 months, followed by boosters at age 15–18 months and 4–6 years).

As I mentioned earlier, uptake of vaccinations that protects against whooping cough has fallen in recent years. This is a particularly important issue for two groups of adults who should receive booster doses—pregnant women and those over 65 years-of-age.

Pregnant women should be offered a whooping cough vaccine in every pregnancy, ideally between 20 and 32 weeks. This vaccination passes antibodies to the fetus so the baby can be protected from birth. (In the first months of life, before they can receive their own vaccines, babies are most vulnerable to severe pertussis.)

People over age 65 are the second group of adults who should be routinely given a DTaP booster. This is because vaccine-induced immunity wanes with age leaving older adults particularly susceptible to the severe complications of whooping cough.

Older adults, especially those fortunate enough to be prospective or new grandparents, should also sign up for a DTaP booster so if they get infected they won’t pass B. pertussis on to their grandkids. And at the same time they get a DTaP jab, they will also bolster their immunity against two other life-threatening bacterial infections: diphtheria and tetanus.