Overview
Although it's considered a vaccine-preventable disease, whooping cough (pertussis) certainly hasn't been eliminated as a public health problem. While most other diseases that are vaccinated against in childhood are decreasing in frequency, cases of whooping cough actually increased through the 1980s.
Canada has about 7,000 reported cases a year. In unvaccinated populations, about three-quarters of all cases occur in children under five, and nearly 40% in babies less than six months old. While there are no Canadian mortality statistics, we know from American figures that mortality is over 1% in children under 1 year old. Because the effects of the vaccination wear off, adults are susceptible to the disease.
Causes
Whooping cough is caused by the bacterium Bordetella pertussis.The bacterium is transmitted in tiny droplets that come from the nose and mouth and is spread from person to person. A similar bacterium called Bordetella parapertussis causes a milder version of whooping cough known as parapertussis.
While 71% of cases of pertussis occur in children under 5 years, it may be that the majority of carriers are older. One infection with this bacterium doesn't provide lifelong immunity, but it does mean subsequent infections are unlikely to cause symptoms. It's now believed that adults are a major source of infection in infants.
Since many people reach adulthood without having been infected, it's entirely possible for adults to develop whooping cough. One Canadian study concluded that between 10% and 20% of coughs in adults and adolescents that last seven days or more are caused by pertussis. After infants, the people most likely to suffer serious complications from whooping cough are seniors and those with chronic ill health.
The disease takes one or two weeks to incubate. People become infectious to others by the end of the first week and they typically remain contagious for about six weeks. The disease is highly contagious and you will be advised to avoid contact with others while you are still able to infect people.
Symptoms
The disease has three stages. The first stage (catarrhal stage) begins about 10 days after infection, and causes symptoms like a common cold - sneezing, tears, tiredness, and loss of appetite. There's also a dry hacking cough.
The second stage (paroxysmal stage) occurs after 10 to 14 days and is signalled by a rapid increase in the frequency and severity of coughing. It's this cough that gives the disease its name. Half a dozen or more rapid coughs follow each other in quick succession, followed by a "whooping" sound as the person inhales deep and fast. It may happen hundreds of times in a single day. The coughing may produce large amounts of thick mucus. Sometimes infants swallow it, but it may exit through the nostrils, often forming bubbles. Frequent coughing and mucus can cause vomiting, and choking is a risk in infants. Infants are actually less likely to make the whooping sound than are older children or adults, but they're more likely to have a choking spell.
After a month, most people start to look and feel better and cough less. This is the third stage (convalescent stage) - a gradual recovery taking a few weeks or occasionally a few months. The usual total course of the disease lasts 6 to 10 weeks.
The risk of complications is highest in infants under one year old. There's also potential danger to seniors and those with chronic ill health. The most common complication in children is otitis media, a middle ear infection. Other complications include pneumonia, encephalitis (inflammation of the brain), seizures, apnea (brief periods when breathing stops), and hemorrhages (bleeding) in the eye.
Treatment
Although bacteria cause whooping cough, antibiotics aren't especially effective in treating it unless they're given in the first stage. Very often, the disease isn't recognized until it enters the second stage. Nevertheless, antibiotics such as erythromcyin*, clarithromycin, azithromycin, or sulfamethoxazole - trimethoprim are given at this stage to reduce the possibility of complications, even if they don't cut the duration of the whooping cough itself.
Infants with pertussis are often hospitalized, especially those less than six months of age. Treatment is designed to minimize symptoms and the damage those symptoms can cause. In the case of heavy vomiting, fluids and sodium must be replaced intravenously. In babies, it may be necessary to suck out mucus with a vacuum-like device or to install a nasal breathing tube to help breathing. Extra oxygen may also be necessary. Expectorant and cough-suppressing medications are generally not recommended. Babies with pertussis should be left to sleep as much as possible, since any disturbance or excitement is likely to trigger coughing. In older children, symptoms and risks are much milder, and hospitalization is hardly ever needed.
Most people know there's a vaccine against whooping cough; however, too many people know about it for the wrong reasons. Anti-vaccine groups and the media have focused on a one-in-a-million chance of encephalitis (severe brain inflammation) occurring in the hours or days after the vaccination, while not addressing the far larger risk of encephalitis caused by whooping cough in unvaccinated people.
The last sizeable Canadian outbreak of pertussis, in New Brunswick in 1998, was overwhelmingly concentrated in the 5 to 14 age group. This was a clear sign that vaccinations were allowed to lapse, because vaccinations given in infancy would have worn off by these ages.
The Canadian pertussis vaccination schedule is as follows: babies are given the DPT (diphtheria-pertussis-tetanus) vaccine at two months, four months, and six months of age to establish basic immunity. They are then given boosters at 18 months and at four to six years of age. The last booster should cover them to about age 14 to 16, when they stop taking the whooping cough vaccine and switch to the adult diphtheria-tetanus formulation. The first five shots (from 2 months to 4 to 6 years) will usually be given in conjunction with polio vaccine and Hemophilus influenzae B or "Hib" vaccine (an anti-pneumonia vaccine), since these have the same schedule as DPT.
There's a new pertussis vaccine that doesn't contain whole killed Bordetella pertussis cells. The new vaccine is known as DTaP ("a" stands for acellular), while the old one is called DTwP ("w" is for whole). The new shot is even less likely to cause severe reactions than the old one. Because of recent evidence that many infants catch pertussis from adults, aP (acellular pertussis vaccine) is now available in a combined adult diphtheria-tetanus-acellular pertussis shot.
*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For more information on brand names, speak with your doctor or pharmacist.
Other tips:
Whooping cough is usually easy to diagnose. A cotton swab on the end of a wire is inserted through the nostril into the nasopharynx (the breathing tube behind the nose), and then cultured to look for bacteria. About 85% of the time, the bacteria will show up on this test. This means a few cases won't be diagnosable in the early stages, but once it gets to the second stage, the symptoms will make the nature of the condition obvious. In some cases, the disease runs a milder course and the later symptoms do not develop. People who have been immunized can still get whooping cough, but they will have much milder symptoms. Chest x-rays may also be taken to check for the presence of fluid or mucus in the lungs.
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