How to Diagnose Pertussis at the Bedside

Spoon Feed
I couldn't state it better than the author's conclusion: "In adult patients, the presence of whooping or posttussive vomiting should rule in a possible diagnosis of pertussis, whereas the lack of a paroxysmal cough or the presence of fever should rule it out. In children, posttussive vomiting is much less helpful as a clinical diagnostic test."

Why does this matter?
We see lots of patients with cough and often the diagnosis is bronchitis, which doesn't need an antibiotic.  But some patients with persistent cough have pertussis.  How can you tell the difference?  Diagnostic testing for pertussis may take days to weeks to come back.  We have to decide to treat empirically.  But are there clinical signs to clue us in that a patient has pertussis as opposed to viral bronchitis, for which an antibiotic is not indicated?  That's why this paper is helpful.

Whooping and hollerin'
This was a literature search that found 53 papers that dealt with the clinical manifestations of patients with confirmed pertussis.  They found that in adults, the presence of a paroxsymal cough was sensitive for pertussis but non-specific (93% and 21% respectively). And absence of fever was similarly sensitive but not specific (82% and 19%, respectively). Whoop with cough was specific but not sensitive (80% and 30%, respectively).  Post-tussive emesis was similarly specific but not sensitive (78% and 33%, respectively).  In children, post-tussive emesis had only mild sensitivity and specificity (60% and 66%, respectively). How should we use this?  If an adult has a coughing illness with fever or without paroxysmal cough, then you can rule out pertussis. If an adult whoops with cough and vomits after coughing, consider pertussis ruled in and give them azithromycin.  If a child has a coughing illness, it is much harder to rule it out or in.  My practice is to consider the child's duration of illness, family exposure history, vaccination status, severity of illness, and frequency of post-tussive emesis and make the best decision you can with limited information.  In children < 1 year, also strongly consider pertussis if the history includes apnea or cyanosis.  A quick word on vaccination status - immunity wanes in 2-4 years now that we universally use the acellular pertussis vaccine.

Source
Clinical Characteristics of Pertussis-Associated Cough in Adults and Children: A Diagnostic Systematic Review and Meta-Analysis.  Chest. 2017 Aug;152(2):353-367. doi: 10.1016/j.chest.2017.04.186. Epub 2017 May 13.

Peer reviewed by Thomas Davis, MD.

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