February 2022

The Generalist: Pertussis

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Steven V. -

The PCR for Pertussis is 90% sensitive during the first week of illness when we would never order this test then drops to only 10% sensitivity by week 3! So the pcr will not usually be helpful by the time we know this is Pertussis!! If you wait for 4-6 weeks pertussis antibodies IgA and IgM can often be helpful in this situation. Please discuss

Adrien S. -

Thanks for bringing this up, Steven. This certainly is a tricky situation since, like you said, the sensitivity of a nasopharyngeal PCR drops down significantly over time. As per the CDC: (https://www.cdc.gov/pertussis/clinical/diagnostic-testing/diagnosis-confirmation.html) they recommend doing NP PCR swab if the patient is within the first 3 weeks and possibly up to 4 weeks of cough onset. They also recommend doing their single point serology test if the patient is 2-8 weeks and possibly up to 12 weeks post cough onset. A few issues though. First, serology results are not valid if the patient has received an acellular pertussis vaccine within the last 1 year (https://pubmed.ncbi.nlm.nih.gov/21069406/) . Second, there appear to be other (non-CDC developed) commercially available serology tests that have not been validated. So, best to check with your local/state/provincial public health guidelines. Where I am, in Ontario, Canada, serology is not included in the guidelines.

Rabbott -

In 1971-72 I did my last year of medical school at newly opened med school at Memorial University of Newfoundland. "The Rock" was pretty isolated and presumably underimmunized. We had an infectious disease ward at the Janeway Children's hospital where I (we were pretty short on actual house officers) cared for a bunch of kids with pertussis who were dramatic not only for their cough, but for their bright red eyes from the subconjunctival hemorrhages. Plenty of facial petechiae, too. Biggest clinical issue was hydration and nutrition - not enough time to eat or drink between coughs.

Another Bordetella story: My veterinarian friends tell me that they are very familiar with humans (especially veterinarians and staff) getting a milder version of whooping cough when dogs with kennel cough, often caused by bordetella bronchiseptica, share it with their humans. It seems to not infect humans easily, so seems most commonly shared by "lap dogs" and by cats, who get right up to the humans' face and then cough or (in the cats' case) sneeze in the humans face. Like B. pertussis, the cough from B. bronchiseptica last a long time (personal experience, experimental group of me). The human medical literature has little to say about this. If you ask your prolonged cough patients if they have a pet with a recent URI, you will, as I have, occasionally get a positive answer. As an academic, you can really "WOW" the residents with this one.

Adrien S. -

I love a good anecdote. Thanks for sharing these!

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