Whooping cough ( or ), also known as pertussis or the 100-day cough, is a highly contagious, vaccine-preventable bacterial disease caused by the bacterium Bordetella pertussis. Initial symptoms are usually similar to those of the common cold with a runny nose, fever, and mild cough, but these are followed by two or three months of severe coughing fits. Following a fit of coughing, a high-pitched whoop sound or gasp may occur as the person breathes in. The violent coughing usually lasts 1–6 weeks but can last 10 or more, hence the phrase "100-day cough". The cough may be so hard that it causes fatigue, vomiting, and rib fractures. Children less than one year old may have little or no cough and instead have periods when they cannot breathe. The incubation period is usually seven to ten days. Disease may occur in those who have been vaccinated, but symptoms are typically milder. The bacterium Bordetella pertussis causes pertussis, which is spread easily through the coughs and sneezes of an infected person. People are infectious from the start of symptoms until about three weeks into the coughing fits. Diagnosis is by collecting a sample from the back of the nose and throat. This sample can then be tested either by culture or by polymerase chain reaction. Prevention is mainly by vaccination with the pertussis vaccine. Initial immunization is recommended between six and eight weeks of age, with four doses to be given in the first two years of life. Protection from pertussis decreases over time, so additional doses of vaccine are often recommended for older children and adults. Vaccination during pregnancy is highly effective at protecting the infant from pertussis during their vulnerable early months of life, and is recommended in many countries. Antibiotics may be used to prevent the disease in those who have been exposed and are at risk of severe disease. In those with the disease, antibiotics are useful if started within three weeks of the initial symptoms, but otherwise have little effect in most people. In pregnant women and children less than one year old, antibiotics are recommended within six weeks of symptom onset. Antibiotics used include erythromycin, azithromycin, clarithromycin, or trimethoprim/sulfamethoxazole. Evidence to support interventions for the cough, other than antibiotics, is poor. About 50% of infected children less than a year old require hospitalization and nearly 0.5% (1 in 200) die. An estimated 16.3 million people worldwide were infected in 2015. Most cases occur in the developing world, and people of all ages may be affected. In 2015, pertussis resulted in 58,700 deaths – down from 138,000 deaths in 1990. Outbreaks of the disease were first described in the 16th century. The bacterium that causes the infection was discovered in 1906. The pertussis vaccine became available in the 1940s.
Signs and symptoms
The classic symptoms of pertussis are a paroxysmal cough, inspiratory whoop, and fainting, or vomiting after coughing. The cough from pertussis has been documented to cause subconjunctival hemorrhages, rib fractures, urinary incontinence, hernias, and vertebral artery dissection. Violent coughing can cause the pleura to rupture, leading to a pneumothorax. Vomiting after a coughing spell or an inspiratory whooping sound on coughing almost doubles the likelihood that the illness is pertussis. The absence of a paroxysmal cough or posttussive emesis makes it almost half as likely. The illness usually starts with mild respiratory symptoms, including mild coughing, sneezing, or a runny nose (known as the catarrhal stage). After one or two weeks, the cough typically develops into uncontrollable fits, sometimes followed by a high-pitched "whoop" as the person tries to inhale. About 50% of children and adults "whoop" at some point in diagnosed pertussis cases during the paroxysmal stage. This stage usually lasts up to 3 months, or sometimes longer. A gradual transition then occurs to the convalescent stage, which usually lasts one to four weeks. A decrease in paroxysms of coughing marks this stage, although paroxysms may persist for months after the onset of pertussis particularly with subsequent respiratory infection. Symptoms of pertussis can be variable, especially between immunized and non-immunized people. Immunized people can present with a milder infection; they may only have the paroxysmal cough for a couple of weeks and may lack the "whooping" characteristic. Although immunized people have a milder form of the infection, they can still spread the disease to others who are not immune.
Incubation period The time between exposure and the development of symptoms is on average 7–14 days (ranging 6–20 days), and rarely as long as 42 days.
Cause The bacterium Bordetella pertussis causes whooping cough. It is an airborne disease (through droplets) that spreads easily through the coughs and sneezes of an infected person.
Host species Humans are the only host species of B. pertussis. Outbreaks of whooping cough have been observed among chimpanzees in a zoo and wild gorillas; in both cases, it is considered likely that the infection was acquired as a result of close contact with humans. Several zoos have a long-standing custom of vaccinating their primates against whooping cough.
Mechanism After the bacteria are inhaled, they initially adhere to the ciliated epithelium in the nasopharynx. Surface proteins of B. pertussis, including filamentous hemagglutinin and pertactin, mediate attachment to the epithelium. The bacteria then multiply. In infants, who experience more severe disease, the bacteria spread down to the lungs. The bacteria secrete several toxins. Tracheal cytotoxin (TCT), a fragment of peptidoglycan, kills ciliated epithelial cells in the airway and thereby inhibits the mechanism which clears the airways of mucus and debris. TCT may contribute to the cough characteristic of pertussis. Pertussis toxin causes lymphocytosis by an unknown mechanism. The elevated number of white blood cells leads to pulmonary hypertension, a major cause of death by pertussis. In infants who develop encephalopathy, cerebral hemorrhage and cortical atrophy occur, likely due to hypoxia.
Diagnosis
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