pertussis, whooping cough

Pertussis is a disease which was once very common in this country. It was brought under some degree of control; now it seems to be increasing in incidence again. This fact has brought renewed interest in trying to control this disease. To give a little perspective, in 1923, 9,000 people died of pertussis. In the 1930s, there were about a quarter of a million cases of pertussis per year. Immunization began in the 1930s; by 1970 the number of cases had fallen to about 1,000 per year. By the late 1980s, pertussis started its comeback in the US, with numbers of cases peaking in the several thousands in several recent years.

The causative organism is usuallythe bacterium Bordatella pertussis, but sometimes the related organism Bordatella parapertussis. In the unvaccinated person, the disease lasts 6 to 10 weeks. Classically, the disease has three stages: catarrhal, paroxysmal, and convalescent. After an incubation period of 3-12 days, the patient develops cold symptoms - a clear runny nose, sneezing, perhaps some fever. This is the catarrhal phase. As these symptoms wane, the child begins to develop a dry, hacking cough, which builds in intensity over time. As the cough progresses in severity, the least stimulation or startle can trigger a long paroxysm of hacking cough which ends in a sharp drawing in of the breath - the "whoop." Post-cough vomiting is classic and very suggestive of the diagnosis. Between paroxysms of coughing, the children appear well. This is the paroxysmal phase. Gradually these symptoms abate in the convalescent phase.

Infants have the highest hospitalization and complication rates. Fifty percent or more of infants who contract pertussis are hospitalised. Twenty-five percent develop pneumonia; four percent develop seizures, one percent suffer permanent brain damage and another one percent die. Pertussis infection in the very small infant might also be implicated in some apparent SIDS cases.

Symptoms af adult pertussis generally do not include the "whoop," but can include the paroxysms of severe cough, postcough vomiting, urinary incontinence (!), pneumonia, and otitis media. Broken ribs are very common in full-blown adult pertussis. Imagine coughing hard enough to break your ribs.

Young children who get pertussis usually catch it from adults. The pertussis germ is widespread in the adult population, a fact unknown to parents and unfortunately, to many doctors who care for adults. For example, 26% of those students at the University of California at Los Angeles who had a cough that lasted more than five days had pertussis. Very similar percentages have been found around the developed world. Doctors who care for adults rarely even consider the diagnosis of pertussis in an adult unless the patient has a classic whoop at the end of the cough - a symptom which can often be absent. They generally refuse to consider the diagnosis even if the patient himself mentions it (imagine that - a doctor not listening to the patient...)! Yet another study showed that 20% of adult patients with any cough lasting more than a week were blood test positive for pertussis infection.

"It should be suspected when an illness thought to be a cold is associated with the development of a paroxysmal cough that worsens at night and is nonproductive. Between coughing attacks, the patient with pertussis has no symptoms; this fact is useful in differentiating pertussis from cough illnesses caused by respiratory viruses or allergic conditions." - James D.Cherry, MD, MSc, Ann Intern Med.1998;128:64-66
This means that your child is very likely to come into contact numerous times with adults who are actively spreading the infection. Adults suspected of having pertussis should be treated with erythromycin for 14 days. Early treatment will shorten the course of the illness and eliminate the risk for transmission.

Mothers with even mild symptoms are able to transmit the disease to very young infants. Unfortunately, the first dose or two of vaccine does not confer full immunity. The primary series and the fourth booster must be completed to fully protect your child. My last case of confirmed pertussis was in a five month old girl who had already had two DTP shots. She was "mildly" ill - she only coughed for three or four weeks and was "only" in the hospital for a week.

Unfortunately, pediatric immunization alone will never eradicate this terrible disease. Pertussis immunization wears off as we age, creating the large pool of susceptible adults. In addition, it is clear that immunity even after infection is not lifelong, and strangely, it seems that this type of naturally acquired immunity is inferior to that induced by immunization. Adult pertussis is very common in Germany, for example, where many patients get pertussis as children, then suffer from the same disease again in adulthood; these patients have more severe disease than that suffered by American adults who were immunized and later were infected when their immunity wore off.

Since 1955 there has been discussion of the possible need to re-vaccinate adolescents and adults. Since that time, it has been thought that the side effects of the vaccine in older individuals outweighed the possible benefits. Now, with the advent of several acellular (purified split-cell) vaccines, these concerns seem outweighed by the possible benefits of booster immunization. The new acellular vaccines are very well tolerated by adults, with very few minor side effects. We are now immunizing all adolescents with the tetanus/acellular pertussis vaccine for the tetanus booster.

Experts are not ready to recommend universal pertussis re-vaccination for adults, but are studying the issue. It is more likely that a campaign for vaccination of high risk individuals such as pregnant mothers will be the result.

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