Pertussis (Whooping Cough)

Symptoms

• Catarrhal phase (1-2 weeks): mild URI symptoms — rhinorrhea, low-grade fever, mild cough; most contagious period
• Paroxysmal phase (2-8 weeks): sudden severe coughing fits ending with inspiratory whoop and post-tussive emesis; cyanosis with paroxysm; afebrile between fits
• Convalescent phase (weeks to months): gradual reduction in frequency and severity
• Adolescents/adults often have ATYPICAL presentation: prolonged cough (≥2 weeks) without classic whoop
• Infants <6 months: may present with apnea WITHOUT classic cough — 'whoop' less common; high risk of death

Signs / physical exam

• Between paroxysms: often appears well
• During paroxysm: facial plethora, cyanosis, subconjunctival hemorrhage, lacrimation, post-tussive emesis
• Inspiratory whoop (classic in children; uncommon in adults and young infants)
• Generally afebrile (high fever suggests alternative diagnosis or complication)

Classic findings

Paroxysmal coughing fits with inspiratory whoop and post-tussive emesis lasting >2 weeks in a child or adolescent. Apnea (not cough) in young infant.

Diagnostic criteria

CDC clinical case definition: cough ≥2 weeks with paroxysms, inspiratory whoop, OR post-tussive emesis without other apparent cause. Laboratory confirmation: positive culture, PCR, or seroconversion.

Labs

• Nasopharyngeal swab/aspirate for B. pertussis PCR (highest sensitivity in first 3-4 weeks of cough)
• Bacterial culture on Bordet-Gengou or Regan-Lowe medium (specific but slow and lower sensitivity; useful for surveillance and antimicrobial susceptibility)
• Serology (anti-pertussis toxin IgG) — useful later in illness (>2-4 weeks); positive in vaccinated patients may be confounding
• CBC — marked LYMPHOCYTOSIS classic (especially infants and unvaccinated children); WBC >20,000 with lymphocyte predominance
• Pertussis case reporting to public health is mandatory in the US

Imaging

• Chest radiograph: often normal or shows perihilar infiltrate ('shaggy heart border'); rules out pneumonia and other complications

First-line

• Antibiotic treatment primarily REDUCES TRANSMISSION; clinical benefit greatest if started in catarrhal or early paroxysmal phase
• Macrolide first-line:
• Azithromycin: infants <1 month 10 mg/kg/day × 5 days; older children/adults 500 mg day 1 then 250 mg days 2-5
• Clarithromycin or erythromycin alternatives (avoid erythromycin in infants <1 month due to pyloric stenosis risk)
• Macrolide alternative if intolerant or resistant: TMP-SMX (NOT for infants <2 months due to kernicterus risk)
• Supportive care: hydration, nutritional support, gentle suctioning of secretions
• Hospitalize infants <6 months and those with severe disease (apnea, cyanosis, dehydration, complications)
• Treat as soon as suspected; do not wait for confirmation in high-suspicion cases
• Bronchodilators, corticosteroids, antitussives NOT effective
• Isolation (droplet precautions) until 5 days of effective antibiotic therapy completed; if untreated, until 21 days of cough

Second-line / adjunct

• Post-exposure prophylaxis (same antibiotic regimen as treatment) for all household contacts and high-risk contacts (infants <12 months, late pregnancy, healthcare workers caring for infants/pregnant women), regardless of vaccination status
• Pregnant women should receive Tdap during each pregnancy (preferably 27-36 weeks) — passive antibody transfer protects newborn before infant vaccinations
• Routine childhood vaccination: DTaP at 2, 4, 6, 15-18 months and 4-6 years
• Adolescent and adult Tdap booster (single dose ≥age 11, then Td or Tdap every 10 years)
• Cocoon strategy — vaccinate close contacts of newborns