Pertussis

Background

• 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

• 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)

Treatment

• 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

References

• 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]