Pertussis a growing grown-up problem

When Perri Klass, MD, associate professor of pediatrics at Boston University School of Medicine, became congested and couldn't stop coughing, she figured she had her annual case of "pediatric crud" -- an occupational hazard of seeing sick kids all day in the middle of winter. After a couple weeks when she still couldn't stop coughing, she started thinking about the possibility of pertussis.

"It was the worst cough I'd ever had, and it wasn't going away," she said.

Her internist assured her that pertussis was highly unlikely and suggested that the cough was the result of a lingering viral illness. Her doctor took a sample anyway, and sent it off to the lab.

As it turned out, pertussis was exactly what she had. Thus, Dr. Klass became one of the growing number of physicians -- and adult patients -- who are learning that this illness can hit those older than 18 and is doing so with more frequency, primarily because of waning vaccine immunity.

"It's harder to recognize in adults, but doctors need to think of it and think of it earlier rather than later," said Dr. Klass, who wrote about her experience in the May 13, 2004 New England Journal of Medicine.

Interrupting the spread

The number of pertussis cases has nearly doubled in the past decade, according to the Centers for Disease Control and Prevention. And, whereas adults used to comprise only a tenth of the total, they now make up more than a quarter. The uptick has led more physicians and public health officials to make presentations at medical meetings and publish papers to raise suspicion that an adult's chronic cough may be more.

"Pertussis has been the sleeping giant that really has awakened because waning immunity may have caught up with the population. Physicians for adults need to give the disease its due," said Mark Dworkin, MD, MPHTM, state epidemiologist at the Illinois Dept. of Public Health, who wrote a perspective piece on the issue in the May 17 Annals of Internal Medicine.

Experts say detection is key, not so much for the patient who will usually get better eventually without intervention but to interrupt spread -- particularly to infants, for whom the infection could be deadly. Many believe the jump in cases among unvaccinated infants can be partially blamed on the increasing adult incidence.

Pertussis is a reportable illness, and an accurate diagnosis allows public health workers to trace contacts and provide prophylaxis antibiotics as appropriate to interrupt this cycle. "What's nice is that when you report a case, public health takes over," said Ralph Gonzales, MD, MSPH, associate professor of medicine, epidemiology and biostatistics at the University of California, San Francisco. He has treated several adults with the condition. "The local health department is aggressive at following up on cases."

Meanwhile, anecdotal evidence suggests that doctors are now more aware of the possibility of adult cases, but there are other barriers to detection. For example, testing for this condition is not standardized from lab to lab and not considered reliable.

"It has started to be on the list of possible diagnoses," said James Nordin, MD, MPH, a pediatrician and clinical investigator at HealthPartners in Minneapolis who has researched this issue. "But the test sensitivity is very poor."

Testing every patient with a persistent cough would find too few cases to be worth the effort. But who among the chronic coughers? Experts emphasize that risk factors such as exposure to sick children be given greater regard than the symptoms, which tend to be more nonspecific.

"That's the most challenging part for internists," Dr. Gonzales said. "We don't know who to test. Adults don't whoop."

Many also question whether the increase in cases reported to the CDC is a true spike or the result of improvements in detection and diagnostic technology. "I'm not so sure we have an epidemic," Dr. Gonzales said. "It could be detection bias."

But experts say prevention of spread is not the only reason that physicians who care for adults should be alert to this disease. There is also the possibility of a vaccine for this age group in the very near future.

Boostrix, a vaccine which combines protection against pertussis, diphtheria and tetanus, was approved by the Food and Drug Administration in May for adolescents, and this nod could potentially be expanded to those who are older. Adacel, a similar vaccine that could be used in people up to age 64, was OK'd by an FDA advisory panel earlier this year. The agency is not bound by its committee's recommendations but usually follows them. Public health officials believe a vaccine for adults could ultimately mean the end of pertussis.

"We are heading towards adult vaccination," Dr. Dworkin said. "Since this is a disease that is only found in humans, we might be able to eliminate or eradicate it."