06 June 2012

Harrison's Ch. 148: "Pertussis and Other Bordetella Infections"

While I read the 397 chapters of Harrison's Principles of Internal Medicine, I am writing reflections.

From Chapter 148:
Pertussis is an acute infection of the respiratory tract caused by Bordetella pertussis. The name pertussis means "violent cough," which aptly describes the most consistent and prominent feature of the illness. The inspiratory sound made at the end of an episode of paroxysmal coughing gives rise to the common name for the illness, "whooping cough."...The Chinese name for pertussis is "the 100-day cough," which accurately describes the clinical course of the illness.

In two weeks, I examined two patients who I was rather certain had pertussis. They had recently begun having coughing fits lasting several minutes. Their lungs sounded clear, and neither was feverish. The fits were so severe that it kept them up at night, and sometimes the force of the coughing fits made them vomit. This last feature, known as post-tussive emesis (literally, vomiting after coughing), is a trademark of pertussis. Whooping cough wasn't a perfect fit--both patients had been vaccinated against pertussis, and neither could recall being exposed to someone with the illness. But nothing else seemed to fit very well, either

We obtained a nasal swab from both patients and sent it to the lab. Both times, the test came back negative! This was quite aggravating. Did I go wrong somewhere?

It's important to note that no test is perfect. This particular test for pertussis has a 90% sensitivity, meaning that only 90% patients with pertussis would have a positive result. Still, this means that the likelihood of two patients having pertussis both getting negative test results is only 1%.

Maybe the specimens weren't collected properly? I reviewed the CDC's guidelines. I hadn't left the swab in one patient's nose for as long as recommended. The swabs weren't refrigerated during transport, which could have potentially caused problems. But even these potential missteps don't seem like they would change the tests' outcome by much.

So was it pertussis? Was it another disease that I didn't think of? Were my textbooks wrong?

These are not just philosophical questions. When a patient has pertussis, not only are they given heavy-duty antibiotics, but so is everyone living in their household. The antibiotics have side effects and can breed resistance. Proper treatment here requires knowing the probability that a patient has the disease.

Medicine is full of ambiguities. I don't know what my patients had, and therefore, I don't know whether the treatment helped them or made things worse. In most cases, I have to learn to be OK with that.