What is whooping cough?

Causes and Symptoms

The etiological agent of whooping cough is Bordetella pertussis, a small, gram-negative, rod-shaped bacterium. A similar organism, Bordetella parapertussis, causes a less severe form of the disease. Symptoms and tissue damage are the result of a toxin secreted by the organism.

The diagnosis of pertussis is primarily clinical, based on the characteristic whoop that accompanies the paroxysmal stage. The most definitive diagnosis involves the actual isolation of the organism. Most pathogenic strains of Bordetella are fastidious in their requirements. Nasal swabs from the patient are obtained, with the organism grown on a special Bordet-Gengou medium.

The clinical manifestation of whooping cough is arbitrarily divided into the catarrhal, paroxysmal, and convalescent stages. The average incubation period following exposure is about seven days. During this period, the patient develops a dry cough, often accompanied by sneezing. A mild fever may be present. Early symptoms resemble those of bronchitis or influenza.

The severity of the cough gradually increases over the next ten to fourteen days; it may be triggered by exercise or even eating. As the patient enters the paroxysmal stage, the cough becomes deeper and more pronounced. It is often characterized as a series of short bursts, followed by a whooping sound as the patient attempts to inhale; the sound itself is caused by possible spasm of the epiglottis.

Large quantities of mucus may be expelled during the coughing spells, which in severe cases may occur forty to fifty times a day. The patient may exhibit dyspnea and become cyanotic from lack of air. In infants, choking is common during this stage and can prove fatal. The severity of the cough has also been known to result in hemorrhaging from the throat.

The paroxysmal stage of the disease lasts from four to six weeks. Gradually, the cough disappears as the patient enters the convalescent stage. The entire period of illness may last ten weeks, with the cough persisting for months afterward; coughing may recur during another respiratory illness.

The disease is highly contagious, with the agent passing from person to person by means of respiratory droplets. The patient is most infectious during both the catarrhal stage and the early portion of the paroxysmal stage, a period lasting two to three weeks.

Treatment and Therapy

Routine treatment of whooping cough consists of bed rest and the provision of adequate food and water. Infants are most at risk and are generally hospitalized. The administration of oxygen may be helpful in the relief of dyspnea and cyanosis. If there is prolonged vomiting, intravenous therapy may be necessary. Administration of corticosteroids has also been shown to ameliorate the severity of the cough.

Because paroxysmal symptoms are associated with production of a toxin secondary to the initial infection, antibiotics are of little help. An antibiotic such as erythromycin, however, may be administered to reduce secondary infections or to limit transmission to other persons. If erythromycin is administered early during the development of the disease, during the incubation period, or even during the first week of the catarrhal stage, it may prevent the disease or limit its severity. Persons coming into contact with the patient should also receive a course of antibiotic treatment.

Immunoglobulin is available, but its effectiveness is in dispute. Active immunization with pertussis vaccine is recommended to protect against the initial infection. Usually, this is a portion of the DTaP vaccine administered in a series of injections beginning at about two months of age.

Perspective and Prospects

The earliest known description of whooping cough was that by G. Baillou in 1578. It was Robert Watt, an English physician, who in 1813 provided the first complete clinical description of the disease. Watt also described the results of autopsies that he had performed on children who had died of the disease during his thirty years of observations; two of these children were his own. Watt also noted the highly contagious nature of whooping cough.

In 1906, Jules Bordet and his brother-in-law, Octave Gengou, isolated the infectious agent from the sputum of Bordet’s son, who had contracted the disease. Known initially as Haemophilus pertussis, the organism was eventually renamed Bordetella pertussis after its discoverer. Bordet also determined that the virulent nature of the disease resulted from the production of a toxin. The special substance needed to grow the organism in the laboratory became known as Bordet-Gengou medium.

Initial attempts to develop a pertussis vaccine by Bordet and Gengou using inactivated toxin were largely unsuccessful. In the 1940s, however, an inactivated whole cell suspension was introduced and proved effective in immunizing children against the disease. In the United States, the pertussis vaccine was combined with inactivated diphtheria and tetanus preparations into a trivalent vaccine, DPT, that proved effective in immunizing children against all three diseases simultaneously.

Because of side effects in some children receiving the pertussis preparation, such as fever, vomiting, and mild seizures, questions developed as to the safety of the vaccine. In 1997, a new vaccine, DTaP, was introduced after researchers learned it was much less likely to cause the adverse reactions found with the DPT vaccine. The a in DTaP stands for “acellular,” which means there are no whole bacteria in the vaccine. While the DPT vaccine uses whole, inactivate pertussis bacteria, the DTaP uses only the parts of the bacteria that help children develop immunity to it. Since human beings represent the only reservoir of whooping cough, the disease may eventually face eradication.

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