Pertussis toxin helps it to evade the host defenses
Pathophysiology
Four steps to infection: attachment, evasion of host defenses, local damage, and systemic manifestations
Virulence determined by filamentous hemagglutinin (FHA) and fimbriae (FIM) adhesins
Required for tracheal colonization
Pertussis toxin (PT) also plays a role
Adenylate cyclase toxin (ACT) and PT allow it to evade host defenses
ACT inhibits macrophages by catalysing ATP to cAMP
PT delays neutrophil recruitment by suppressing G protein signaling pathways
Tracheal cytotoxin (TCT) produces NO and damages the tracheal epitheleal cells
Few systemic manifestations because it doesn't enter circulation
Clinical Manifestations
Presents with cough lasting 14 days or more, with paroxysms of coughing, an inspiratory whoop, and post-tussive vomiting
Incubation period of 7 to 10 days on average (range 5 to 21 days)
Young Children
Three stages:
Catarrhal stage, with rhinorrhea, nonpurulent conjuctivitis, occasional cough, and a low-grade fever; lasts 1 to 2 weeks.
Paroxysmal stage, with fits of coughing and an inspiratory whoop; lasts 1 to 6 weeks. May have post-tussive emesis. Occasionally associated with hyperinsulinemia and hypoglycemia in infants.
Convalescent stage, with the cough slowly resolving over 1 to 6 weeks, occasionally up to 8 weeks.
Adults
Can present atypically, with less whooping and less post-tussive vomiting
Coughing is seen in most patients, lasting longer than 21 days
Mean duration 36 to 48 days
Post-tussive vomiting is suggestive of pertussis
Carrier State
Transient nasopharyngeal carriage in immunized children
Complications
Case-fatality rate of 1% in children under 6 months
Pneumonia is the most common complication, either caused by the disease itself for by coinfection (especially RSV)
Encephalopathy is a rare complication, usually in unimmunized children
Begins weeks 2 to 4 after cough, with seizures and focal neurologic deficits
Pulmonary hypertension
Pneumonia and urinary incontinence are common in older patients
The paroxysms of coughing can also cause subconjunctival hemorrhages, syncope, and rib fractures
Diagnosis
Nasopharyngeal swab/aspirate culture
Sensitivity 15 to 80%
PCR
Serology
Antibodies (IgG and IgA) against GHA, agglutinogen, or PT
IgG rises 2 to 3 weeks after infection or immunization (1 week after booster)
Look for a two-fold increase in IgG to diagnose acute infection
Antigens including PT
Management
Treat within 21 days of symptom onset (except if <1 mo. old, treat regardless of duration)
In children
Azithromycin 10 mg/kg on day 1 followed by 5 mg/kg/d for 4 days
Erythomycin 40-50 mg/kg/d divided qid for 7-14 days