Whooping cough

Whooping cough is a highly contagious disease caused by the bacteria Bordatella pertussis. It is characterized by classic paroxysms (spasms) of uncontrollable coughing, followed by a sharp intake of air which creates the characteristic "whoop" of the disease name.

B. pertussis is uniquely a human pathogen, meaning that it neither causes disease in other animals, nor survives in humans without resulting in disease. It exists worldwide as a disease-causing agent, and causes epidemics cyclically in all locations.

B. pertussis causes its most severe symptoms by attacking specifically those cells in the respiratory tract which have cilia. Cilia are small, hair-like projections which beat constantly, and serve to constantly sweep the respiratory tract clean of such debris as mucus, bacteria, viruses, and dead cells. When B. pertussis interferes with this normal, janitorial function, mucus and cellular debris accumulate and cause constant irritation to the respiratory tract, triggering the cough reflex and increasing further mucus production.

Children under the age of two, particularly infants, are most at risk for serious infection , although the disease can occur at any age. However, once an individual has been exposed to B. pertussis, subsequent exposures result in mild illness similar to the common cold, and thus usually not identifiable as resulting from B. pertussis.

Symptoms and progression of whooping cough

Whooping cough has four somewhat overlapping stages: incubation, catarrhal stage, paroxysmal stage, and convalescent stage.

An individual usually acquires B. pertussis by inhaling droplets infected with the bacteria, coughed into the air by an individual already suffering from whooping cough symptoms. Incubation is the period of seven to 14 days after exposure to B. pertussis, and during which the bacteria penetrate the lining tissues of the entire respiratory tract.

The catarrhal stage is often mistaken for an exceedingly heavy cold. The patient has teary eyes, sneezing, fatigue, poor appetite, and a very runny nose. This stage lasts about 10-14 days.

The paroxysmal stage, lasting two to four weeks, is heralded by the development of the characteristic whooping cough. Spasms of uncontrollable coughing, the "whooping" sound of the sharp inspiration of air, and vomiting are hallmarks of this stage. The whoop is believed to occur due to inflammation and mucous which narrow the breathing tubes, causing the patient to struggle to get air in, and resulting in intense exhaustion. The paroxysms can be caused by overactivity, feeding, crying, or even overhearing someone else cough.

The mucus which is produced during the paroxysmal stage is thicker and more difficult to clear than the waterier mucus of the catarrhal stage, and the patient becomes increasingly exhausted while attempting to cough clear the respiratory tract. Severely ill children may have great difficulty maintaining the normal level of oxygen in their systems, and may appear somewhat blue after a paroxysm of coughing due to the low oxygen content of their blood . Such children may also suffer from encephalopathy, a swelling and degeneration of the brain which is believed to be caused both by lack of oxygen to the brain during paroxysms, and also by bleeding into the brain caused by increased pressure during coughing. Seizures may result from decreased oxygen to the brain. Some children have such greatly increased abdominal pressure during coughing, that hernias result (hernias are the abnormal protrusion of a loop of intestine through a weaker area of muscle). Another complicating factor during this phase is the development of pneumonia from infection with another bacterial agent, which takes hold due to the patient's weakened condition.

If the patient survives the paroxysmal stage, recovery occurs gradually during the convalescent stage, and takes about three to four weeks. Spasms of coughing may continue to occur over a period of months, especially when a patient contracts a cold or any other respiratory infection.

Children who die of pertussis infection usually have one or more of three conditions present: 1) severe pneumonia, perhaps with accompanying encephalopathy; 2) extreme weight loss, weakness, and metabolic abnormalities due to persistent vomiting during paroxysms of coughing; 3) other pre-existing conditions, so that the patient is already in a relatively weak, vulnerable state (such conditions may include low birth weight, poor nutrition , infection with the measles virus , presence of other respiratory or gastrointestinal infections or diseases).

Diagnosis

Diagnosis based just on symptomatology is not particularly accurate, as the catarrhal stage may appear to be a heavy cold, a case of the flu, or bronchitis . Other viruses and tuberculosis infections cause symptoms similar to those found during the paroxysmal stage. The presence of a pertussis-like cough along with an increase of certain specific white blood cells (lymphocytes) is suggestive of B. pertussis infection, although it could occur with other pertussis-like viruses. The most accurate method of diagnosis is to culture (grow on a laboratory plate) the organisms obtained from swabbing mucus out of the nasopharynx (the breathing tube continuous with the nose). B. pertussis can then be identified during microscopic examination of the culture.

Treatment

Treatment with the antibiotic erythromycin is helpful only at very early stages of whooping cough: during incubation and early in the catarrhal stage. After the cilia, and the cells bearing those cilia, are damaged, the process cannot be reversed. Such a patient will experience the full progression of whooping cough symptoms, which will only abate when the old, damaged lining cells of the respiratory tract are replaced over time with new, healthy, cilia-bearing cells. However, treatment with erythromycin is still recommended to decrease the likelihood of B. pertussis spreading. In fact, all members of the household in which a patient with whooping cough lives should be treated with erythromycin to prevent spread of B. pertussis throughout the community.

Other treatment is supportive, and includes careful monitoring of fluids, rest in a quiet, dark room to decrease paroxysms, and suctioning of mucus.

Prevention

The mainstay of prevention lies in the mass immunization program which begins in the United States when an infant is two months old. The pertussis vaccine , most often given as one immunization together with diphtheria and tetanus , has greatly reduced the incidence of whooping cough. Unfortunately, there has been some concern about serious neurologic side effects from the vaccine itself. This concern led huge numbers of parents in England, Japan, and Sweden to avoid immunizing their children, which in turn led to major epidemics of disease in those countries. Multiple carefully constructed research studies, however, have disproved pertussis vaccine as the cause of neurologic damage.

See also Childhood diseases; Respiratory diseases; Respiratory system.

Resources

books

Berkow, Robert, and Andrew J. Fletcher. The Merck Manual of Diagnosis and Therapy. Rahway, NJ: Merck Research Laboratories, 1992.

Kobayashi, G., Patrick R. Murray, Ken Rosenthal, and Michael Pfaller. Medical Microbiology. St. Louis: Mosby, 2003.

Krugman, Saul, et al. Infectious Diseases of Children. St. Louis: Mosby-Year Book, Inc., 1992.

Rosalyn Carson-DeWitt

KEY TERMS

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Cilia

—Tiny, hair-like projections from a cell. In the respiratory tract, cilia beat constantly in order to move mucus and debris up and out of the respiratory tree, in order to protect the lung from infection or irritation by foreign bodies.

Encephalopathy

—Any abnormality in the structure or function of the brain.

Pathogen

—A disease causing agent, such as a bacteria, virus, fungus, etc.