Pertussis (whooping cough) is caused by Bordetella pertussis, a bacterial pathogen for which humans serve as the only known host. Although a vaccine for pertussis was developed over 80 years ago, this disease remains a leading cause of vaccine-preventable deaths in the world.
While 90% of all cases occur in third-world countries, Canada still experiences a relatively high number of cases, Australia recently reported an epidemic, and pertussis is the only vaccine-preventable disease that has recently caused an increase in deaths in the United States. (Centers for Disease Control and Prevention. Outbreak Notice: Pertussis in Australia. April 17, 2009, and Gregory D. Pertussis: a disease affecting all ages. Am Fam Phys 2006;74[3]:420-26)
Pertussis occurs in all age groups, but over two-thirds of cases occur in children under five years of age, and nearly 40% of all cases, including nearly all of the deaths, occur in infants less than six months old. (Pertussis in The Merck Manual, 18th Edition. 2006:1465-67)
Waning Immunity and Fear of Vaccination Allow Pertussis to Persist
Smallpox, another infectious agent whose only natural host is humans, was eradicated in 1977, mainly due to global immunization efforts. The vaccine for smallpox only had to be administered once because the immunity it conferred waned over years to decades.
Conversely, the vaccine for pertussis confers immunity that is much shorter in duration: Five doses – administered at 2, 4, and 6 months of age, and then boosted at 15 to 18 months and 4 to 6 years of age – are required to maintain adequate immunity until adulthood, when the disease is typically less severe.
Therefore, to attain an adequate level of “herd immunity” in a given population, all infants and children must adhere to a fairly strict vaccination schedule, and adolescents and adults must be immunized to prevent them from serving as a reservoir for the disease.
To make matters worse, the original pertussis vaccine contained cellular components of the bacterium, and immunization was associated with significant side effects, including:
- Persistent, inconsolable crying or screaming
- Seizures
- Anaphylaxis
- Fever over 104.5º F (40.5º C)
- Encephalopathy
- Cardiovascular collapse and shock
It wasn’t until 1981 that an a cellular vaccine (i.e., one that did not contain cellular components) first became available in Japan and then found its way to other developed nations. Alas, the fear of pertussis vaccination was well entrenched in the minds of many parents, even though the new formulation dramatically reduced the incidence of adverse events. (Pichichero M, et al. Combined tetanus, diphtheria, and 5-component pertussis vaccine for use in adolescents and adults. JAMA 2005;293:3003-3011)
Unfortunately, the cheaper cellular pertussis vaccine is still used in third-world countries, and immunized persons in poorer regions still suffer from side effects associated with this preparation.
What Does Whooping Cough (Pertussis) Look Like?
Following initial infection by B. pertussis, a one- to three-week incubation period ensues as the organism invades the cells of the respiratory tract and begins to produce a bacterial toxin.
Disease onset is then heralded by a cold-like syndrome (the catarrhal stage) characterized by sneezing, runny nose, tearing, and a hacking, nocturnal cough.
After 10 to 14 days, the paroxysmal stage begins, and the cough becomes increasingly forceful and frequent. Repeated, spasmodic bouts of coughing occur, during which the patient is unable to draw breath. As a paroxysm ends, the characteristic, hurried, deep inspiration occurs (the “whoop”), and this is typically followed by another paroxysm of coughing.
Infants may exhibit choking spells instead of the classic whooping inhalation following coughing spasms. Even slight disturbances, such as turning a patient or switching on a light, can trigger paroxysms of cough.
During coughing episodes, thick, sticky mucus may be expelled from the nostrils; it is not uncommon for patients – particularly infants – to become hypoxic and cyanotic during coughing spells, and suffocation is a common cause of death in younger patients.
For survivors, the convalescent stage begins a month or so after disease onset. The average duration of the illness lasts seven to eight weeks, but paroxysms of coughing may recur for several months.
Frequent complications of pertussis include:
- Bronchopneumonia, which can be fatal at any age
- Otitis media (middle ear infection)
- Seizures
- Hemorrhage into the eyes, skin, mucous membranes and brain
- Rectal prolapse due to severe cough
- Toxic encephalitis with resultant mental retardation and spastic paralysis in survivors
- Death occurs in 2% of children under one year of age
Can Whooping Cough (Pertussis) be Treated?
The administration of antibiotics in the catarrhal stage may lessen the effects of pertussis, but the disease mimics a common cold during this early stage, so its seriousness may not be recognized.
Once the paroxysmal stage begins, antibiotics do not benefit the sick individual, but they are typically administered anyway to limit the spread of pertussis to other individuals.
Quarantine – usually for about four weeks – is enforced for patients who are not critically ill. For the seriously ill, hospitalization, isolation, and respiratory support (including intubation and artificial ventilation) are mainstays of treatment.
Owing to idiosyncrasies in the human response to vaccination for Bordetella pertussis and persistent fears of side effects from older forms of the pertussis vaccine, whooping cough remains a serious disease...even in wealthy, industrialized nations.
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