Family Medicine Board Review Course 2019

A 17-year-old girl presents with a "bad cough" that has lasted for 2-3 weeks. How much should the presence or absence of any of the 3 classic pertussis symptoms—paroxysmal cough, post-tussive whoop, and post-tussive emesis—strengthen or weaken a clinical concern for pertussis?

 "Paroxysmal cough" is commonly reported both by patients who do and do not have pertussis; its presence does not significantly increase the likelihood of pertussis.
 The absence of an inspiratory whoop is more powerful in ruling out pertussis than the absence of a paroxysmal cough.
 The presence of all 3 classic pertussis symptoms simultaneously doubles the likelihood of a pertussis diagnosis.
 The absence of all 3 classic pertussis symptoms is highly predictive of the absence of pertussis.

Correct Answer:

"Paroxysmal cough" is commonly reported both by patients who do and do not have pertussis; its presence does not significantly increase the likelihood of pertussis.

Educational Objective:

Discuss factors that should increase a concern for pertussis in an adolescent with a persistent cough.

Key Point:

Studies show that the symptom of "paroxysmal cough" is commonly reported by both patients who do and do not have pertussis. Therefore, the presence of just a "paroxysmal cough" by itself is a fairly insensitive indicator for pertussis (likelihood ratio [LR] is close to 1).

Explanation:

The presence/absence of most classic pertussis symptoms only modestly increases/decreases the probability of pertussis (with the presence of paroxysmal cough by itself being nearly meaningless either for or against a pertussis diagnosis); clinicians need to consider the clinical context when deciding about the need to test and/or treat for pertussis.

More specifically:

In a teenager with cough, the presence of a "paroxysmal cough" by itself is not a sensitive indicator for pertussis. The presence of either of the other 2 pertussis symptoms in isolation – "post-tussive emesis" or "whoop"-- each modestly raises the likelihood that the patient has pertussis (LR of 1.8 and 1.9, respectively).

The absence of any of the 3 classic pertussis symptoms modestly decreases a patient's likelihood of having pertussis, with the absence of paroxysmal cough (LR = 0.52) being the most predictive of the absence of pertussis, followed by post-tussive emesis (LR = 0.58), and finally (weakest association) inspiratory whoop (LR = 0.78).

Unfortunately, no study to date has investigated the predictive power of multiple pertussis symptoms being simultaneously present or absent.

References:

Cornia PB, Hersh AL, Lipsky BA, Newman TB, Gonzales R. Does this coughing adolescent or adult patient have pertussis? JAMA. 2010;304(8):890-896.

Liang JL, Tiwari T, Moro P, et al. Prevention of Pertussis, Tetanus, and Diphtheria with Vaccines in the United States: Recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Morb Mortal Wkly Rep. 2018;67(2):1–44.

Pertussis (Whooping Cough). Centers for Disease Control and Prevention.  7 Aug. 2017, Accessed 26 Feb 2019.

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