How do you diagnose Bordetella (B.) pertussis in pediatric patients?

Diagnosing Bordetella Pertussis in Pediatric Patients

The most appropriate diagnostic approach for B. pertussis in pediatric patients is nasopharyngeal sampling for PCR testing, which offers 80-100% sensitivity and should be performed within the first 2 weeks of illness onset. 1

Clinical Suspicion

When evaluating a child with suspected pertussis, consider:

• Key clinical features that warrant testing:

  • Paroxysmal cough (93.2% sensitivity but only 20.6% specificity)
  • Post-tussive vomiting
  • Inspiratory whoop (particularly in older children)
  • Apnea (more common in infants <2 years than whooping) 2, 1
  • Known exposure to confirmed pertussis case

• Age-specific presentations:

  • Infants: May present with apnea rather than classic whooping cough
  • Older children: More likely to have classic paroxysmal cough
  • Adolescents/partially immunized: May have atypical presentation with persistent cough as the only symptom 2

Diagnostic Testing Algorithm

1. First-line testing: Nasopharyngeal specimen collection

   • Timing: Ideally within first 2 weeks of cough onset (before day 25 of symptoms)
   • Collection method: Dacron or polyester swab of nasopharynx (not throat swab)
   • Testing options:
     • PCR testing (preferred): 80-100% sensitivity 2, 1
     • Culture: Gold standard for definitive diagnosis but lower sensitivity (25-50%) 1

2. Serologic testing (less useful clinically):

   • Consider if cough duration >2 weeks when PCR sensitivity decreases
   • Requires paired sera (acute and convalescent)
   • Specificity 99%, sensitivity 63% 2, 1
   • Limited utility since patients often present late in illness course

Common Pitfalls to Avoid

• Delayed specimen collection: Sensitivity decreases after 2 weeks of symptoms
• Improper technique: Ensure proper nasopharyngeal sampling (not just throat swab)
• Testing after antibiotic administration: Reduces likelihood of positive culture
• Relying solely on clinical diagnosis: Clinical features have high sensitivity but low specificity 1
• Failure to consider pertussis in vaccinated children: Partial immunity can modify presentation

Special Considerations

• Infants <4 months: Highest risk group for severe disease and mortality 3

  • May present with leukocytosis (>20,000 WBC/mm³)
  • Leukocytosis >30,000 WBC/mm³ is a predictor of mortality (RR 6.7) 4
  • Consider pertussis in any infant with marked leukocytosis and respiratory symptoms

• Co-infections: B. pertussis can co-occur with viral pathogens (particularly RSV)

  • In one study, 67% of pertussis cases also had RSV 5
  • Consider pertussis testing in bronchiolitis cases not responding to standard treatment 6

Case Definitions

• Confirmed case: Isolation of B. pertussis OR PCR-positive OR clinical case with epidemiological link to confirmed case
• Probable case: Persistent cough >2 weeks with paroxysms, post-tussive vomiting, or inspiratory stridor without another apparent cause 1

Public Health Considerations

• All suspected and confirmed cases should be reported to public health authorities
• Treatment should begin as soon as pertussis is suspected, without waiting for test results 1

Remember that early diagnosis facilitates prompt treatment and appropriate isolation measures, which are critical for preventing transmission, especially to vulnerable unvaccinated infants who have the highest risk of severe disease and mortality.