Whooping cough, better known as pertussis to microbiologists and infectious-diseases specialists, is the cunning work of Bordetella pertussis. Although physically small by bacterial standards, the organism possesses weapons that would put a medieval dungeon master to shame. From filamentous attachment spines to toxins that paralyze and kill cells, the species is well equipped for wreaking havoc in the human respiratory tract. Its hallmark, in fact, is a redundancy of weaponry. After an infection is successfully established, several types of toxins temporarily stun the host’s immune cells, thereby protecting the invading organisms and also prolonging their siege.
Early on, however, the invader causes symptoms remarkably like that of the common cold: runny nose, watery eyes, sore throat, fatigue. It usually takes at least one to two weeks before a pertussis infection has so colonized and injured the airways that it provokes a run of explosive coughs, each lasting more than a minute. Patients gasp for air afterward, hence the legendary “whoop.” Meanwhile, they may carry on with their normal lives, often sharing the infection with unsuspecting schoolmates, friends, and coworkers.
Ironically, by the time the warning sounds, the patient’s immune system has brought the infection under some control. It’s during the early, nonspecific phase of infection that Bordetella pertussis is most contagious, most easily cultured from the nose and throat, and most easily treated, usually with an erythromycin-type antibiotic. By the time a patient develops a paroxysmal cough and finally gets to a doctor, the trail is cold; a culture will typically show no sign of infection, and only specialized tests can prove the recent presence of the culprit. Thus many cases—especially infections of adolescents and adults—are never diagnosed and treated.
But even with antibiotic treatment, the violent coughing fits can last four to six weeks, occasionally causing infants and youngsters to suffer such dramatic consequences as eye, nose, and brain hemorrhages as well as rib fractures and hernias. Infants under 1 year old with pertussis are also prone to seizures, apnea (pauses in breathing), and a temporary decline in mental function called encephalopathy. A final complication in babies is malnutrition-nonstop coughing robs them of time and energy to eat, sometimes resulting in skin-and-bones starvation. Adults like Jean, on the other hand, rarely lose more than a few pounds.
Meanwhile, my friend was surprised—and puzzled—by my diagnosis.
“Pertussis—what an interesting idea! But I was vaccinated in childhood. Shouldn’t I still be immune?”
“Not necessarily. It’s a short-lived vaccine that’s only given in childhood, even today. When we were kids, the final pertussis booster was given around age 7. By the time you entered medical school, your protection was probably gone.”
“Wow. I thought pertussis was ancient history here.”
Jean’s mistaken impression was familiar. Until a year earlier, I had held the same belief. But then I read a research study involving college students on our own campus-the University of California at Los Angeles. The undergraduates had come to the student health service with a persistent cough of six days’ or greater duration. Of 130 subjects evaluated over 30 months, 26 percent had evidence of recent infection with Bordetella pertussis. Whooping cough was alive and well in our own backyard. Just as in Jean’s case, the students’ childhood shots protected them for a decade or two, but certainly not for a lifetime.
Like a good scientist, Jean wanted some evidence. And after six weeks of symptoms, both she and I knew that a culture swab was not likely to produce it. But we had another method. We could look for pertussis antibodies, the same way the students had been diagnosed in the study. A week later, Jean’s blood test returned unequivocally positive. I hadn’t been able to alleviate her suffering, but at least I had given her an answer.