Author: Michelle Lin, MD
Updated: 9/3/2010



  • Bordetella pertussis – Gram negative coccobacillus
  • Childhood vaccination confers immunity for 5-10 years
  • Incubation period: 7-10 days

CDC Clinical Case Definition of Pertussis

Cough illness lasting ≥ 2 weeks without other apparent cause with 1 or more of:

  • Cough paroxysms
  • Posttussive emesis
  • Inspiratory whoop
Finding Positive LR Negative LR
Paroxysmal cough 1.1 (1.1-1.4) 0.52 (0.14-0.58)
Posttussive emesis 1.8 (1.7-1.9) 0.58 (0.49-0.80)
Inspiratory whoop 1.9 (1.8-2.4) 0.78 (0.46-0.87)

Phases of Pertussis

Phase 1: Catarrhal (week #0-2)

  • Nonspecific URI symptoms
  • Afebrile or low-grade temperature
  • Excessive lacrimation, conjunctival injection

Phase 2: Paroxysmal (week #2-8)

  • Paroxysmal coughing spells
  • Minimal symptoms between paroxysms
  • May hear inspiratory “whoop” especially in children and infants
  • Posttussive emesis or syncope

Phase 3: Convalescent (week #8-12)

  • Persistent or improving cough


  • Diagnosis is not easy
  • Dacron swab of posterior nasopharynx (cotton swab is toxic to B pertussis)
  • PCR assay (results in 1-2 days, more costly)
  • DFA is inexpensive but poorly sensitive and specific (not recommended)


  • Macrolide (e.g. azithromycin), or trimethoprim-sulfamethoxazole (if allergic)
  • Antibiotics decrease duration of pertussis course if given in catarrhal stage (but difficult to differentiate from viral URI)
  • Antibiotics in any stage decreases transmission to others.

American Academy of Pediatrics (AAP) recommendation for patients <3 months old:

  • If suspect pertussis (basically a cough), swab for pertussis and start azithromycin immediately (10 mg/kg per day in a single dose x 5 days).

Bottom Line

  • Positive and negative LR’s for clinical findings are not very helpful.
  • More dependent on your pretest probability of patient having pertussis.
  • Check if there is a current outbreak in your region.

Fagan Nomogram

Fagan nomogram


  • Cornia PB, Hersh AL, Lipsky BA, Newman TB, Gonzales R. Does this coughing adolescent or adult patient have pertussis? JAMA. 2010 Aug 25;304(8):890-6. [PubMed]