Glossary of Medical and Health Terms

Whooping Cough (Pertussis)

Whooping cough (pertussis) is a highly contagious disease caused by the bacterium Bordetella pertussis. The characteristic severe hacking cough is followed by an intake of breath that sounds like 'whoop'. A similar, milder disease is caused by B. parapertussis. The whoop is "high-pitched", in babies and children only. Pertussis is one of the leading causes of vaccine-preventable deaths worldwide. There are 30-50 million pertussis cases per year, with 90% in the developing world. About 300,000 die each year, despite generally high coverage with the DTP and DTaP vaccines. Most deaths occur in young infants who are either unvaccinated or incompletely vaccinated; three doses of the vaccine are necessary for complete protection against pertussis. Children tend to catch it more than adults. Pertussis in infants and young children is characterized initially by mild respiratory infection symptoms such as cough, sneezing, and runny nose (catarrhal stage). After one to two weeks, paroxysms of coughing followed by an inspiratory "whooping" sound (paroxysmal stage) develop. Vomiting due to the violence of the coughing fit may occur. In severe cases, the recurrent vomiting can lead to malnutrition and dehydration. Coughing fits occur spontaneously but can also be triggered by yawning, stretching, laughing, or yelling. The fits gradually diminish over one to two months. Complications include pneumonia, encephalitis, pulmonary hypertension, and secondary bacterial superinfection.

Pertussis is spread by contact with airborne discharges from the mucous membranes of infected people, who are most contagious during the catarrhal stage. However due to non-specific symptoms, pertussis is usually not diagnosed until the appearance of the characteristic cough of the paroxysmal stage. For diagnosis, bacterial samples can only be recovered during the first three weeks of illness, rendering culturing and DFA useless after this period. (Although PCR may have some limited usefulness for an additional three weeks.) For adults and adolescents who often delay seeking medical advice, serology is used to determine whether antibody against pertussis toxin or another component of B. pertussis is present at high levels in the blood of the patient. Erythromycin or azithromycin are effective antibiotics, which shorten the infectious period but not the outcome of the disease. Symptoms may be lessened if treatment is initiated in the catarrhal stage. Close contacts exposed to respiratory secretions of an infected person in the 21 days before or after the infected person's cough began, may be protected from developing symptomatic disease if they receive appropriate antibiotics (chemoprophylaxis) during the 7-21 day incubation period.

A pure culture of B. pertussis was isolated in 1906 by Jules Bordet and Octave Gengou, who also developed the first serology and vaccine. The complete B. pertussis genome of 4,086,186 base pairs was sequenced in 2002. Neither vaccination nor infection confers long-term immunity so infection of adolescents and adults who have been vaccinated or infected previously is also common. Any residual immunity may reduce symptoms to a prolonged cough. However any infected adults and adolescents remain the major source of transmission to unimmunized or partially immunized infants who are at greatest risk of severe complications from pertussis. Pertussis vaccines are highly effective, strongly recommended, and save many infant lives every year. As protection lasts only a few years, the vaccines are staged so that immunity lasts through childhood, the time of greatest exposure and greatest risk. Tetanus, diphtheria and whooping cough are given in combination at ages 2, 4, and 6 months, then at 15-18 months, 4-6 years and 11 years. Although Canada, France, the U.S. and Germany now have approved booster shots for adolescents, adults, or both, other countries still stop after the age of seven because of concerns that side effects associated with the first available "whole-cell" pertussis immunizations tended to increase with age.

Controversy surrounded the DTP (Diptheria/Tetanus/Pertussis), vaccine in the 1970s and 1980s - whether the whole-cell pertussis component caused permanent brain injury in rare cases. Although well established that the pertussis component of the DTP vaccine accounted for most of the minor local and systemic side effects in many vaccinated infants, several published studies failed to show a causal relationship between administration of the DTP vaccine and permanent brain injury. However, criticism of these studies and well-publicized anecdotal reports of DTP-induced permanent disability and death gave rise to anti-DTP movements. In addition, a number of children suffered allergic reactions to the pertussis vaccination, including severe seizures. Despite this, doctors recommended the vaccine, and even threatened parents who refused to vaccinate their children. By the late 1970s, publicity caused the immunization rate to fall in several countries, including Great Britain, Sweden, and Japan resulting in a dramatic increase in the incidence of pertussis. Yuji Sato introduced a safer acellular pertussis vaccine for Japan in 1981. Nevertheless, other countries continued to use the whole-cell DTP.

In the U.S., low profit margins and increased lawsuits led many manufacturers to stop producing the DTP vaccine by the early 1980s. To avert a vaccine crisis, Congress in 1986 passed the National Childhood Vaccine Injury Act (NCVIA), which vaccines. Prices of vaccines have since stabilized, and the number of lawsuits dwindled. (The majority of claims were allegedly caused by the whole-cell DTP vaccine.) The acellular pertussis vaccine was approved in the U.S. 1992 for use in the combination DTaP vaccine. Research has shown the acellular vaccine to be safe, with few reports of adverse effects. Whole-cell DTP vaccine is no longer used in the U.S but is still purchased by the World Health Organization for developing nations because it is much cheaper than acellular DtaP vaccine.

Before vaccines, an average of 157 cases per 100,000 persons were reported in the U.S., with peaks reported every two to five years; incidence was likely much higher. After vaccinations were introduced in the 1940s, incidence fell dramatically to less than 1 per 100,000 by 1970. Incidence rates have increased somewhat since 1980. Pertussis is the only vaccine-preventable disease that is associated with increasing deaths in the U.S. The number of deaths increased from 4 in 1996 to 17 in 2001, almost all of which were infants under one year. The discontinuation of booster vaccination in older persons has created a large pool of older persons lacking immunity, with an increase of adult-onset pertussis that accelerated beginning in about 2004. With this rise, newborns are at risk of exposure to pertussis before the infants' vaccinations can be completed. The decision to resume vaccinating teens and adults reflects in part that the newer acellular vaccine DTaP has greatly reduced the incidence of adverse effects observed with the earlier "whole-cell" pertussis vaccine. An acellular vaccine preparation for adults and adolescents has been approved in Canada, Europe, and the United States. In the U.S., the Food and Drug Administration has authorized both the use of the vaccines Boostrix (GlaxoSmithKline) for 10-18 year olds in May 2005 and Adacel (Sanofi Pasteur) for 11-64 year olds in August 2005. (Not suitable for those with a history of adverse reaction to the whole-cell pertussis vaccines.)

Associated ICD-10 codes: A37.

Source: http://en.wikipedia.org/wiki/Pertussis

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