Whooping Cough (Pertussis)
Whooping Cough (Pertussis)
Whooping cough is also known as pertussis, a word that means “intense cough.” It is caused by the bacterium Bordetella pertussis, which is a pathogen (disease-causing organism) with a propensity for lung tissue. Whooping cough was once the leading cause of death in children under five in the United States. In 1945, it caused more deaths than diphtheria, scarlet fever, measles, and polio combined. Since the introduction of an effective vaccine in the late 1940s, the number of cases of whooping cough has decreased sharply, although there have been increases in recent years.
Whooping cough is no ordinary cough. The disease is marked by bouts of severe spasmodic coughing that end with a characteristic “whooping” sound and vomiting. Complications from secondary bacterial infection include pneumonia and ear infection. Mortality is greatest among infants, especially those who are born prematurely. Whooping cough is a highly contagious disease, so it is important that children be vaccinated against it.
The causative agent of whooping cough is B. pertussis, which is a Gram-negative coccus (a short, rod-shaped bacterium). The term Gram-negative refers to the way the microbe reacts with Gram stain, which is used to prepare samples for microscopy. B. pertussis specifically infects the tissue of the lung, and its incubation period is 6–20 days.
WORDS TO KNOW
ANTIBIOTIC RESISTANCE: The ability of bacteria to resist the actions of antibiotic drugs.
GRAM-NEGATIVE BACTERIA: All types of bacteria identified and classified as a group that does not retain crystal-violet dye during Gram's method of staining.
PAROXYSM: In medicine, a paroxysm may be a fit, convulsion, or seizure. It may also be a sudden worsening or recurrence of disease symptoms.
PATHOGEN: A disease causing agent, such as a bacteria, virus, fungus, etc.
PNEUMONIA: Pneumonia is inflammation of the lung accompanied by filling of some air sacs with fluid (consolidation). It can be caused by a number of infectious agents, including bacteria, viruses, and fungi.
VACCINE: A substance that is introduced to stimulate antibody production and thus provide immunity to a particular disease.
Whooping cough may last for several weeks and is divided into three distinct stages. The catarrhal stage involves non-specific symptoms, such as a runny nose, a mild cough, and a mild fever, which may easily be mistaken for a cold. This stage may continue for a week or so, before the second, so-called paroxysymal stage sets in. This is marked by paroxysms—or attacks—of severe, repetitive coughing ending in a ‘whooping’ sound and vomiting, usually accompanied by exhaustion. The coughing has a choking quality, and the patient's face may look congested. There may be between two and 50 attacks a day, occurring more frequently at night. Between attacks the patient does not usually cough at all.
The whooping sound comes from the larynx or voice box, as the patient finally takes a proper breath in after an attack. Complications of this stage of whooping cough include convulsions and seizures arising from a reduced supply of oxygen to the brain. This is thought to occur either because of the coughing itself or due to a toxin released by B. pertussis. This stage lasts for one to four weeks, during which time secondary bacterial infections like otitis media—an infection of the middle ear— and pneumonia may set in. The latter is the most common and deadly complication of whooping cough.
The final stage of whooping cough is convalescence and is characterized by a fading away of the cough, in both frequency and intensity. Surveillance data in the United States from 1980 to 1989 suggest that the clinical course of whooping cough is complicated by pneumonia in about 22% of cases, by seizures in 3% of cases and by encephalopathy (a swelling of the brain) in about 1% of cases. Mortality in infants aged less than one month was 1.3% and among infants aged 2–11 months was 0.3%. A case of whooping cough usually gives a patient lifelong immunity to further attacks.
Whooping cough is a highly contagious disease, particularly in the catarrhal stage and up to three weeks after the start of the paroxysmal stage. Adults and adolescents, who may have a milder form of the disease, act as a reservoir of infection. The disease is transmitted through coughing and sneezing, which exposes people to infected respiratory secretions.
Whooping cough has been known as a childhood disease for several hundred years. According to the World Health Organization (WHO) there were 39 million cases of whooping cough around the world in the year 2000, with 297,000 deaths. In many countries, regular epidemics occur every three to five years. Those who have not been fully immunized, either because they are too young or for some other reason, are most at risk of dying from whooping cough.
Before the introduction of the whooping cough vaccine, the disease was the leading cause of death from infectious disease in the under-fives in the United States. Outbreaks tend to occur in the United States between July and October, with about one-third of cases being in infants less than six months old and 60% of the total being in the under-five age group. Premature babies are particularly at risk of whooping cough and are more likely to develop complications than older children.
The whooping cough vaccine reduced the number of whooping cough cases 100-fold by 1970, compared to figures for 1945. But there has been an increase since then, with several states reporting epidemics. The increases have been higher among adolescents and adults than among children, suggesting some waning of immunity in the older age groups. In 1996, the year of the last major outbreak, the Centers for Disease Control and Prevention (CDC) reported nearly 8,000 cases, which was the highest number since 1967. Around 5,000–7,000 cases of whooping cough are reported each year to the CDC, and this number is probably fewer than the actual number of cases. In 2003, there were 13 deaths from whooping cough in the United States.
Antibiotics will shorten the course of whooping cough, if given in the early stages of the disease, but do not tend to shorten the paroxysmal stage. However, antibiotic treatment does help prevent the transmission of the disease. Erythromycin is the antibiotic that is usually recommended for the treatment of whooping cough. A major concern is the emergence of strains of B. pertussis that are resistant to antibiotics. Patients with whooping cough readily become dehydrated and should be given plenty of fluids.
The pertussis vaccine is generally given in combination with vaccines against diphtheria and tetanus (the DTP vaccine). The WHO recommends three injection of DTP be given at the ages of six, ten and 14 weeks, with a booster injection between 18 months and six years. Up to half of children receiving the vaccine will become feverish immediately afterwards for up to 24 hours and may have soreness and redness at the site of the injection.
Whooping cough remains a serious health threat for children around the world, which is why joint efforts of the WHO and other agencies are aimed toward universal vaccination for children. As with other diseases, such as diphtheria and polio, the lives of many children around the world are at risk because they have not been vaccinated. In countries where the health infrastructure is weak or lacking, because of socioeconomic and political problems or geographical factors, access to vaccination may be patchy or non-existent. For example, several children died during two outbreaks of whooping cough in 2003 in Badakhshan, a northeastern province of Afghanistan. An emergency team from the Afghan Health Ministry and the WHO mounted a mass distribution of erthyromycin. Badakhshan is mountainous, isolated, and has few health workers. Many children who live there are malnourished. These factors put them at risk of whooping cough and many other infections.
Centers for Disease Control and Prevention. “Pertussis.” October 13, 2005. <http://www.cdc.gov/ncidod/dbmd/diseaseinfo/pertussis_t.htm> (accessed May 3, 2007).
Whoopingcough.net. “Whooping Cough Information.” <http://www.whoopingcough.net/> (accessed May 3, 2007).
World Health Organization. “Pertussis.” <http://www.who.int/immunization/topics/pertussis/en/index.html> (accessed May 3, 2007).