Whooping cough

• 1. The Hundred-Day Cough

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  A child draws a breath after a fit of coughing and the air rushes in with a high-pitched whoop. That sound gives whooping cough one of its names. Doctors call the disease pertussis. People in some places call it the 100-day cough, because the violent coughing usually lasts one to six weeks but can stretch to ten weeks or more. The early days feel ordinary. There is a runny nose, a mild fever, a small cough, the kind of thing anyone would mistake for a common cold. Then come two or three months of severe coughing fits. The fits can be so hard they cause fatigue, vomiting, and even rib fractures. The culprit is a single bacterium, Bordetella pertussis, and humans are the only species it truly calls home. How does so small an organism wring such damage from the body? Why do the most dangerous cases belong to the youngest patients, infants who may barely cough at all? And how did a disease first written about in the 16th century come roaring back in the 21st, even among people who were vaccinated against it?

• 2. What The Cough Does

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  Subconjunctival hemorrhages, hernias, urinary incontinence, and even vertebral artery dissection have all been documented as consequences of the pertussis cough. The force can rupture the pleura and collapse a lung, a condition called pneumothorax. The body pays a steep physical price for fits this violent. The illness moves in stages. It opens with mild respiratory signs, sneezing, a runny nose, a little coughing, a phase known as the catarrhal stage. After one or two weeks the cough turns into uncontrollable fits, sometimes capped by that strained inhaled whoop. About 50 percent of children and adults whoop at some point during the paroxysmal stage, which usually lasts up to three months. A gradual handoff then leads to the convalescent stage, lasting one to four weeks, when the coughing fits slowly ease. The whoop itself is a strong clue but not a guarantee. Vomiting after a coughing spell or an inspiratory whoop almost doubles the likelihood that the illness is pertussis. The absence of a fit-like cough, or of vomiting after coughing, makes pertussis nearly half as likely.

• 3. Inside The Body

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  Filamentous hemagglutinin and pertactin, two surface proteins of B. pertussis, are the grappling hooks the bacterium uses to grab hold. After being inhaled, the bacteria first cling to the ciliated lining of the nasopharynx, then multiply. In infants, who suffer the worst disease, they spread down into the lungs. The bacterium fights with chemistry. Tracheal cytotoxin, a fragment of peptidoglycan, kills the ciliated cells that sweep mucus and debris out of the airway, disabling the body's cleaning system and likely fueling the signature cough. Pertussis toxin triggers lymphocytosis, a surge in white blood cells, by a mechanism still not understood. That flood of cells leads to pulmonary hypertension, a major cause of death from pertussis. In infants who develop encephalopathy, cerebral hemorrhage and cortical atrophy can follow, likely caused by a lack of oxygen. The incubation period, the gap between exposure and the first symptoms, averages 7 to 14 days and ranges from 6 to 20 days, rarely stretching as far as 42.

• 4. Finding It And Treating It

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  A physician's overall impression turns out to be the most effective tool for an initial diagnosis, more reliable than any single sign on its own. In adults with a cough of less than 8 weeks, vomiting after coughing or a whoop supports the diagnosis. In children with a cough of less than 4 weeks, vomiting after coughing is somewhat supportive but not definitive. The laboratory offers harder evidence. Diagnosis relies on a sample taken from the back of the nose and throat, then cultured on Bordet-Gengou medium, run through polymerase chain reaction, examined by direct fluorescent antibody, or checked by serological methods. The bacterium can only be recovered during the first three weeks of illness, which leaves culture and DFA useless afterward, though PCR may stretch its usefulness another three weeks. Antibiotics are the main treatment, with erythromycin, clarithromycin, and azithromycin recommended; newer macrolides are favored for fewer side effects. Timing decides everything. The sensible rule is to treat people over a year old within three weeks of cough onset, and infants and pregnant women within six weeks. Started early, antibiotics cut the duration of infectiousness and prevent spread. Started late, they will not change the course of the illness. For the cough itself, no effective treatment has been developed, and over-the-counter cough medications are discouraged.

• 5. The Smallest Patients

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  About 50 percent of infected children under a year old require hospitalization, and pertussis is fatal in an estimated 0.5 percent, or 1 in 200, of US infants under one year. The disease saves its cruelty for the youngest. First-year infants are also far more likely to develop complications: apneas in 31 percent of cases, pneumonia in 12 percent, seizures in 0.6 percent, and encephalopathy in 0.15 percent. One reason may be the bacterium's ability to suppress the immune system. Babies under one may not cough much at all. Instead they have periods when they simply cannot breathe. That silent danger is why protection has to arrive before they can defend themselves. Vaccination during pregnancy is highly effective at shielding an infant through those vulnerable early months, and many countries recommend it. Preventive antibiotics are also used frequently in those exposed and at high risk of severe disease, such as infants.

• 6. The Vaccine That Fades

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  Half a million lives were saved by the pertussis vaccine in 2002 alone, by one estimate. The World Health Organization and the United States Centers for Disease Control and Prevention recommend it for routine use. Initial immunization is advised between six and eight weeks of age, with four doses in the first two years of life. The multi-component acellular vaccine is 71 to 85 percent effective, with greater protection against more severe strains. The problem is that the protection does not last. A 2011 CDC study indicated protection may last only three to six years, enough to cover childhood, the time of greatest exposure and greatest risk of death. Infection itself grants only incomplete natural immunity; a 2005 study put estimates of infection-acquired immunity at 7 to 20 years and post-vaccination immunity at 4 to 12 years. Widespread immunization reshaped who gets sick. Reported infections shifted away from children aged 1 to 9 and toward infants, adolescents, and adults. Adolescents and adults now act as reservoirs for B. pertussis, often carrying mild or hidden infections and passing them to infants with too few vaccine doses. Older people are frequently the first case in a household and the source for the children around them.

• 7. A Disease That Came Back

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  An estimated 16.3 million people worldwide were infected in 2015, and pertussis caused 58,700 deaths that year, down from 138,000 deaths in 1990. More than 151,000 cases were reported globally in 2018, though many cases go unreported or undiagnosed, especially in developing countries. A 2017 study put the real global burden at 24 million cases a year, with 160,000 deaths among young children and about 90 percent of all cases in the developing world. Epidemics arrive in cycles, every three to five years, in places with vaccination programs and places without. The reason is a slow erosion. Immunity declines in those who were vaccinated or recovered, new susceptible infants are born, and once herd immunity drops below a certain level an epidemic can ignite. The bacterium may also be evolving to slip past vaccine-induced immunity. The United States tells the story in numbers. Before the vaccine, incidence ran between 100,000 and 200,000 cases a year. After the DTP combined vaccine for diphtheria, tetanus, and pertussis arrived in the 1940s, cases fell through the 1950s and 1960s, dropping below 10,000 a year between 1965 and 2003. The 21st-century resurgence is blamed on a mix of waning immunity and bacterial mutations that evade vaccines.

• 8. From Bordet To Sato

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  Jules Bordet and Octave Gengou discovered the bacterium in 1906, and it was later named Bordetella pertussis in Bordet's honor. The two managed to culture B. pertussis and built the first inactivated whole-cell vaccine in 1912, with other researchers following in 1913 and 1914, though these early efforts had limited effect. In the 1920s, Louis W. Sauer developed a vaccine at Evanston Hospital. In 1925, the Danish physician Thorvald Madsen became the first to test a whole-cell vaccine on a wide scale, using it to control outbreaks in the Faroe Islands in the North Sea; two children died shortly after receiving it. An outbreak in Atlanta, Georgia, in 1932 set the next chapter in motion. It prompted pediatrician Leila Denmark to begin studying the disease, and over six years, working with Emory University and Eli Lilly and Company, she developed the first safe and effective pertussis vaccine. In 1942, American scientists Grace Eldering, Loney Gordon, and Pearl Kendrick combined the whole-cell vaccine with diphtheria and tetanus toxoids to make the first DTP combination. To curb the pertussis component's frequent side effects, Japanese scientist Yuji Sato developed an acellular vaccine from purified haemagglutinins secreted by B. pertussis, first used in Japan starting in 1981. There is a quieter epilogue in the wild: outbreaks have been seen among chimpanzees in a zoo and wild gorillas, likely caught from close human contact, which is why several zoos now keep a custom of vaccinating their primates.