Exam Findings in Pertussis
Classic Physical Examination Findings
The physical examination in pertussis is often surprisingly unremarkable between coughing episodes, with the diagnosis primarily relying on observing or eliciting the characteristic paroxysmal cough pattern rather than specific physical signs. 1, 2
Key Clinical Observations During Examination
Paroxysmal coughing is the hallmark finding—a series of rapid expiratory bursts followed by a sudden loud inspiratory sound (the "whoop"), though this classic whoop is frequently absent in adults and previously vaccinated individuals 1, 2
Post-tussive vomiting occurs commonly during or immediately after coughing paroxysms and, when present, has high specificity (77.7%) for pertussis 2
Inspiratory whoop has low sensitivity but high specificity (79.5%) when present, making it highly suggestive of pertussis 2
Conjunctival injection and lacrimation may be observed during the catarrhal phase, along with rhinorrhea 1, 3
Minimal or absent fever is typical—the presence of fever should prompt consideration of alternative diagnoses 2
Normal lung auscultation between paroxysms is common, as pertussis primarily affects the airways rather than causing parenchymal disease 1
Age-Specific Examination Variations
Infants (Most Critical Population)
Apneic episodes may be the predominant finding rather than cough, particularly in infants under 6 months 2, 3
Cyanosis during or after coughing paroxysms 3
Minimal cough with atypical presentation makes diagnosis challenging 2
Adolescents and Adults
Absence of the classic whoop is the rule rather than the exception in previously vaccinated individuals 1, 2
Prolonged paroxysmal cough lasting 4-6 weeks without other specific findings 1
Shortness of breath and tingling sensation in the throat may be reported 1
Physical signs of chronic cough complications including petechiae, subconjunctival hemorrhages, or rib tenderness from cough-related trauma 1
Laboratory Findings (Not Physical Exam, But Relevant)
- Leukocytosis with lymphocytosis, classically described in pertussis, is frequently absent and should not be relied upon for diagnosis 1
Critical Diagnostic Pitfalls
Do not dismiss pertussis in vaccinated patients—the illness presents with milder, atypical symptoms and absent whoop in previously immunized adolescents and adults 2
The catarrhal phase (first 1-2 weeks) shows only nonspecific upper respiratory symptoms indistinguishable from common viral infections, yet this is when patients are most contagious 1, 2, 3
Normal examination between paroxysms does not exclude pertussis—the diagnosis depends on the pattern and duration of cough rather than specific physical findings 1
Infants with minimal cough and apnea represent a high-risk group that can be easily missed 2
Clinical Case Definition for Diagnosis
Cough persisting >2 weeks accompanied by any of the following: paroxysms of coughing, post-tussive vomiting, or inspiratory whooping sound 1, 2
Paroxysmal cough has high sensitivity (93.2%) but low specificity (20.6%)—its absence makes pertussis unlikely 2
Do not wait for laboratory confirmation to initiate treatment when clinical suspicion exists, as early antibiotic therapy prevents transmission even if it doesn't alter the clinical course 2