What are the diagnostic and treatment approaches for differentiating and managing croup versus pertussis?

Diagnostic and Treatment Approaches for Differentiating Croup vs Pertussis

The definitive diagnosis of pertussis requires isolation of Bordetella pertussis from nasopharyngeal culture, while croup is primarily a clinical diagnosis characterized by barking cough and inspiratory stridor that responds to corticosteroids and, in moderate to severe cases, nebulized epinephrine. 1, 2

Clinical Presentation Differences

Croup

• Characterized by barking cough, inspiratory stridor, and hoarseness 2
• Typically affects children 6 months to 3 years of age 2
• Usually presents with acute onset of symptoms 2
• Low-grade fever may be present but is not necessary for diagnosis 2
• Symptoms typically worsen at night 2
• Duration is usually 3-7 days 3

Pertussis

• Characterized by paroxysmal coughing spells followed by an inspiratory "whoop" and/or post-tussive vomiting 1
• Can affect any age but most serious in young infants 4
• Presents in stages: catarrhal (1-2 weeks of mild symptoms), paroxysmal (2-6 weeks of severe coughing), and convalescent (gradual resolution) 1
• Fever is typically absent or minimal 1
• Cough persists for 2-6 weeks or longer 1
• Previously vaccinated individuals may present with milder, atypical symptoms 1

Diagnostic Approach

For Suspected Croup:

• Diagnosis is primarily clinical based on characteristic barking cough and stridor 2
• Laboratory studies are seldom needed 2
• Radiography should be reserved for cases where alternative diagnoses are suspected 2

For Suspected Pertussis:

• Suspect pertussis when cough lasts ≥2 weeks with paroxysms, post-tussive vomiting, and/or inspiratory whooping 1
• Obtain nasopharyngeal aspirate or Dacron swab for culture - this is the definitive diagnostic method 1
• Consider PCR testing, though not universally standardized 1
• For presumptive diagnosis, order paired acute and convalescent sera to detect fourfold increase in IgG or IgA antibodies to pertussis toxin (PT) or filamentous hemagglutinin (FHA) 1
• A confirmed diagnosis can be made with positive culture or compatible clinical picture with epidemiologic linkage to a confirmed case 1

Treatment Approach

For Croup:

• Administer a single dose of oral, intramuscular, or intravenous dexamethasone for all severities of croup 2
• For moderate to severe croup, add nebulized epinephrine (0.5 mL of 2.25% solution diluted in 2.5 mL saline) 2, 3
• Home care includes adequate hydration, humidification, and fever control 3
• Antihistamines, decongestants, and antibiotics have no proven benefit for uncomplicated viral croup 3

For Pertussis:

• Administer macrolide antibiotics (e.g., azithromycin) early in the course of illness to diminish coughing paroxysms and prevent disease spread 1
• Isolate patients for 5 days from the start of treatment 1
• Treatment beyond the first few weeks of illness may be offered but is unlikely to be effective 1
• Do not use long-acting β-agonists, antihistamines, corticosteroids, or pertussis immunoglobulin as they show no benefit 1
• For severe cases, hospitalization may be necessary, especially for infants who are at higher risk for complications such as apnea, pneumonia, seizures, or death 5

Prevention

For Pertussis:

• All children should receive the complete DTaP primary vaccination series 1
• Adolescents should receive a single dose DTaP booster 1
• Adults up to age 65 should receive Tdap vaccine according to CDC guidelines 1, 5

Common Pitfalls and Caveats

• Pertussis is often overlooked in the differential diagnosis of cough illness, especially in adolescents and adults 1
• The characteristic "whoop" may be absent in previously vaccinated individuals, making diagnosis challenging 1
• Antibiotics for pertussis are most effective when administered early in the course of illness; later treatment may not affect symptom duration but still prevents transmission 1, 5
• Croup can be confused with more serious conditions such as epiglottitis, bacterial tracheitis, or foreign body airway obstruction 2
• Pertussis immunity wanes 5-10 years after vaccination, making adolescents and adults susceptible despite childhood immunization 1, 4