“There is a huge reservoir of people carrying pertussis, particularly [in] the adolescent and adult population[s],” says Alison Holmes, MD, a pediatric hospitalist at Concord Hospital, N.H. “And the babies who get really sick from it are the under two- to three-month group who have not yet been immunized or have just been immunized. Because it is so rampant in the adolescent and adult community, those children can still get sick.”
“Unfortunately,” says Dr. Stucky, “what’s happening is that if physicians are not thinking pertussis, they don’t talk about pertussis to that adult patient who … is either around children or has children in the home. So they don’t know to tell that person to watch for these same signs and symptoms in that young infant, who then could have a much more severe outcome from getting [the infection].”
As with most patients who contract illnesses, these patients may never have heard of the disease and unless educated may not understand the implications of the diagnosis. They might realize their disease could spread to family members, “but most people don’t absorb that information and use that information thoughtfully,” says Dr. Stucky. The onus is, therefore, on the physician to warn adult patients specifically about the serious danger that exists for infants in the two- to three-month-old group, who may not have been vaccinated or whose single-vaccination immunity is not adequate protection against the disease.
While the numbers in babies appear to be what they have always been, the incidence has grown in the teen years and even later into adulthood. This is more likely the result of increased testing for pertussis, as opposed to being only due to a true resurgence. Data from studies of adults with prolonged cough revealed that 20% to 25% have serologic evidence of recent pertussis infection.2 Adults are the major reservoir of infection, and infection spreads quickly in a population in a closed environment where droplets spread easily person to person.5
For both teens and adults, testing and immunization with the newly recommended DTaP (diphtheria-tetanus-pertussis)—as opposed to the more limited Td—can help upgrade immunity. Although a patient can recover from pertussis on his or her own within one to two weeks following treatment, the intent of treatment is primarily to limit the spread of disease to others.4-7
The problem when adults get pertussis, says Dr. Holmes, who is also an assistant professor of community and family medicine at Dartmouth Medical School, Hanover, N.H., “is that they often don’t show up complaining about this horrible paroxysmal coughing until they’re about three or four weeks into the illness, and it hasn’t gone away. You go for hours and hours feeling completely fine and wonderful, and why would you bother going to the doctor?”
Babies are most at risk, however. “They often don’t have the energy or the muscle strength, so they just stop breathing instead,” she says.
Mark Dworkin, MD, MPH, TM, the state epidemiologist and team leader for the Rapid Response Team at the Illinois Department of Public Health, is active in outbreak investigation. He wrote a compelling argument for maintaining a high index of suspicion when physicians see adolescent and adult patients who have a cough that has lasted more than two weeks.4
It has been estimated that more than one million cases of pertussis occur in the United States each year; that number has continued to grow for 20 years. From 1990 to 2001, the incidence of pertussis in adults increased by 400%. But many physicians believe that pertussis is only a pediatric illness. A survey of internists in Washington state showed that only 38% of respondents knew about the risk of vaccine fatigue, and just 36% knew that the nasopharyngeal swab is the preferred method for sample collection. Public health professionals were also concerned with the finding that too many pediatricians and nonpediatricians (43% and 41%, respectively) were not able to define a reportable case.