Whooping cough, also known as pertussis, is a highly contagious disease which causes classic spasms (paroxysms) of uncontrollable coughing, followed by a sharp, high-pitched intake of air which creates the characteristic whoop that is reflected in the disease's name.
Whooping cough is caused by a bacteria called Bordetella pertussis . B. pertussis causes its most severe symptoms by attaching itself to those cells in the respiratory tract that have cilia. Cilia are small, hair-like projections that beat continuously 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, cleansing function, mucus and cellular debris accumulate and cause constant irritation to the respiratory tract, triggering coughing and increasing further mucus production.
Whooping cough exists throughout the world. While people of any age can contract the disease, children under the age of two are at the highest risk for both the disease and for serious complications and death. Apparently, exposure to B. pertussis bacteria earlier in life gives individuals some immunity against infection with it later on. Subsequent infections resemble the common cold .
According to the Centers for Disease Control and Prevention, since 1990, the reported incidence of pertussis has increased in the United States. Peaks occur at three to four year intervals. Since 1990, 14 states reported the number of cases of whooping cough to be more than two per 100,000 in the population. A high proportion of those cases occurred in persons aged ten years or older.
Nearly 75 percent of pertussis cases reported worldwide are in children; half of those children affected require hospitalization . Prior to effective immunization programs in the United States, pertussis was the major cause of death from infectious disease among individuals under the age of 14. Because developing countries as of 2004 did not have widespread immunization available, there continue to be about 50 million cases of pertussis every year across the globe, with 300,000 leading to death. About 38 percent of all hospitalizations from pertussis are in babies under the age of six months.
Causes and symptoms
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 someone already suffering with the infection. Incubation is the asymptomatic period (time when no evidence of disease is present) of seven to 14 days after breathing in the B. pertussis bacteria, during which the bacteria multiply and penetrate the lining tissues of the entire respiratory tract.
The catarrhal stage is often mistaken for an exceedingly heavy cold. People have teary eyes, sneezing, fatigue, poor appetite, and an extremely runny nose (rhinorrhea). This stage lasts approximately ten days to two weeks.
The paroxysmal stage, lasting two to four weeks, begins with the development of the characteristic whooping cough. Spasms of uncontrollable coughing, the whooping sound of the sharp inspiration of air, and vomiting are all hallmarks of this stage. The whoop is believed to occur due to inflammation and increased mucus, which narrow the breathing tubes, causing people to struggle to get air into their lungs; the effort results in intense exhaustion. The paroxysms (spasms) can be induced by over activity, feeding, crying, or even overhearing someone else cough .
The mucus that is produced during the paroxysmal stage is thicker and more difficult to clear than the more watery mucus of the catarrhal stage. Affected persons become increasingly exhausted when attempting to clear the respiratory tract through coughing. 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 swelling and degeneration of the brain (encephalopathy), which is believed to be caused both by lack of oxygen to the brain during paroxysms and 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. Another complicating factor during this phase is the development of pneumonia from infection with another agent. The second pathogen successfully invades due to the person's already-weakened condition.
If individuals survive the paroxysmal stage, recovery occurs gradually during the convalescent stage, usually taking about three to four weeks. However, spasms of coughing may continue to occur over a period of months, especially when a person contracts a cold, or other respiratory infection.
When to call the doctor
A physician or other healthcare professional should be contacted during the first two months of life to arrange for immunization. Otherwise, a person with a cough that lasts for more than a few days should be seen by a healthcare professional.
A diagnosis that is based solely on a person's symptoms is not particularly accurate, as the catarrhal stage may appear to be a heavy cold, a case of the flu, or a case of bronchitis . Other viruses and tuberculosis infections can 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 pertussis (whooping cough). However, cough can occur from 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 by examining the culture under a microscope.
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 person experiences the full progression of whooping cough symptoms; symptoms only improve 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 an individual with whooping cough lives should be treated with erythromycin to prevent the spread of B. pertussis throughout the community. The only other treatment is supportive and involves careful monitoring of fluids to prevent dehydration , rest in a quiet, dark room to decrease paroxysms, and suctioning of mucus from the lungs.
Just under 1 percent of all cases of whooping cough in the United States result in death. Children who die of whooping cough usually have one or more of the following three conditions present:
- severe pneumonia, perhaps with accompanying encephalopathy
- extreme weight loss, weakness, and metabolic abnormalities due to persistent vomiting during paroxysms of coughing
- other pre-existing conditions, so that the person is already in a relatively weak, vulnerable state (such conditions may include low birth weight babies, poor nutrition , infection with the measles virus, presence of other respiratory or gastrointestinal infections or diseases)
The mainstay of prevention lies in programs similar to the mass immunization program in the United States that begins immunization inoculations when infants are 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. Three injections (a primary and two booster shots) during early infancy confer complete immunity. Unfortunately, in the 1990s, there has been some concern about serious neurologic side effects from the vaccine itself. This concern led significant numbers of parents in England, Japan, and Sweden to avoid immunizing their children. Such actions led to major epidemics of the disease in those countries. However, several carefully constructed research studies disproved the idea that the pertussis vaccine is the cause of neurologic damage. Furthermore, a subsequent formulation of the pertussis vaccine became available. Unlike the former whole cell pertussis vaccine, which was composed of the entire bacterial cell that has been deactivated (and therefore unable to cause infection), the subsequent acellular pertussis vaccine does not use a whole cell of the bacteria but is comprised of between two and five chemical components of the B. pertussis bacteria. The acellular pertussis vaccine appears to greatly reduce the risk of unpleasant reactions to the vaccine, including high fever and discomfort following vaccination .
Persons with whooping cough should be given adequate nutrition to assist their bodies in recovering from the infective agent.
Cilia —Tiny hairlike projections on certain cells within the body. Cilia produce lashing or whipping movements to direct or cause motion of substances or fluids within the body. Within the respiratory tract, the cilia act to move mucus along, in an effort to continually flush out and clean the respiratory tract.
Encephalopathy —Any abnormality in the structure or function of brain tissues.
Hernia —A rupture in the wall of a body cavity, through which an organ may protrude.
Parents should ensure that their children receive a complete series of immunizations (three injections) against whooping cough. Children who are suspected of having whooping cough should be seen by a healthcare professional. Early treatment is essential to limit the progression of the disease.
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L. Fleming Fallon, Jr., MD, DrPH