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Pertussis (Whooping Cough)

BASICS

  • Highly contagious respiratory illness caused by Bordetella pertussis (and occasionally B. parapertussis)
  • Transmission: Aerosolized droplets; person-to-person
  • Hosts: Humans (all ages; adults are most common reservoir)
  • Distribution: Worldwide; endemic/epidemic with outbreaks every 3–5 years
  • Seasonality: Peaks in late summer-autumn but can occur year-round
  • Vaccine available: Yes, but immunity is not 100% or lifelong (natural or vaccine)
  • Classic triad: Paroxysmal cough, inspiratory whoop, posttussive emesis
  • Nickname: "Cough of 100 days"

EPIDEMIOLOGY

  • Incubation: 7–10 days (range 5–21 days)
  • US Peak (2012): 48,277 reported cases
  • Global: ~24 million cases, 160,700 deaths/year
  • All ages affected; highest morbidity/mortality in infants <6 months

ETIOLOGY & PATHOPHYSIOLOGY

  • Toxin-mediated infection targets ciliated respiratory epithelium
  • Organisms: B. pertussis (main), B. parapertussis
  • No known genetic predisposition

RISK FACTORS

  • Exposure to a confirmed case
  • Non- or under-immunized infants/children
  • Prematurity, chronic lung disease, immunodeficiency (e.g., AIDS)
  • Obesity, pre-existing asthma
  • Infants <6 months: ~90% of pediatric hospitalizations

PREVENTION

  • Immunization:
  • Primary childhood series + boosters
  • Tdap during every pregnancy (27–36 weeks gestation)
  • Cocooning: vaccinate all close contacts of infants <1 year
  • Adults, especially healthcare workers, should be immunized
  • Public health: Surveillance, outbreak management, prophylaxis

ASSOCIATED CONDITIONS

  • Apnea (infants), secondary bacterial pneumonia, sinusitis, seizures, encephalopathy, urinary incontinence, death

DIAGNOSIS

History

  • Recent exposure
  • Insidious onset; classic paroxysmal cough, inspiratory whoop, posttussive emesis
  • Incubation 7–10 days

Physical Exam

  • Catarrhal phase (1–2 weeks): Rhinorrhea, mild cough, low-grade fever
  • Paroxysmal phase (2–6 weeks): Bursts of intense cough, whoop, vomiting after coughing
  • Convalescent phase (weeks): Gradual reduction of cough
  • Note: Infants <6 months may have atypical or severe presentations; adults/unvaccinated children present classically

Differential Diagnosis

  • B. parapertussis, Mycoplasma pneumoniae, Chlamydia spp., RSV, adenovirus, B. bronchiseptica, B. holmesii

Diagnostic Tests

  • Nasopharyngeal culture (gold standard; best within 2 weeks of cough onset)
  • PCR assays: Rapid, accurate in first 3 weeks
  • Serology: Not FDA-approved; commercial assays available
  • Chest X-ray: To evaluate for pneumonia if indicated
  • Consider EEG/neuroimaging if seizures/ALTEs (infants)

TREATMENT

General Measures

  • Hospitalize neonates for monitoring; supplemental O₂, ventilation as needed
  • Isolation: Respiratory precautions for 5 days after antibiotics, or 3 weeks after symptom onset if untreated
  • Supportive care: gentle suctioning, avoid triggers, small frequent feeds, IV fluids if needed

Medication

  • Start empiric antibiotics if strong suspicion/high risk before confirmatory tests
  • First line: Azithromycin (preferred in all ages for treatment & prophylaxis; 5-day course)
  • Other options: Clarithromycin, erythromycin (avoid in infants <1 month)
  • Second line: TMP/SMX (for age >2 months, if macrolide allergy/resistance)
  • Monitor infants <1 month on macrolides for hypertrophic pyloric stenosis; avoid clarithromycin in infants <1 month; avoid TMP/SMX <2 months.

Symptomatic therapies (e.g., corticosteroids, β₂-agonists): Not consistently effective

REFERRAL/ADMISSION

  • Hospitalize infants <6 months, especially premature, unimmunized, or with complications (respiratory distress, apnea, pneumonia, feeding problems, seizures)

ONGOING CARE

  • Monitor for complications (respiratory, neurologic, nutritional)
  • ICU for severe/compromised cases
  • Family education: immunization importance, chemoprophylaxis for contacts

PROGNOSIS

  • Most recover completely
  • Infants <6 months: Highest risk for morbidity & mortality
  • Global deaths: ~160,799/year

COMPLICATIONS

  • Infants: Apnea, cyanosis, sudden death
  • Children: Conjunctival hemorrhage, pneumonia, seizures, hernia
  • Adults: Sinusitis, otitis media, pneumonia, rib fracture, weight loss, fainting, incontinence, seizures, encephalopathy

ICD-10 CODES

  • A37.10: Whooping cough due to B. parapertussis, no pneumonia
  • A37: Whooping cough
  • A37.91: Whooping cough, unspecified species with pneumonia

CLINICAL PEARLS

  • Classic triad: Paroxysmal cough, inspiratory whoop, posttussive emesis
  • Hospitalization risk and mortality highest in infants <4 months
  • Maternal Tdap protects newborns—most effective in first 2 months
  • Immunization or prior infection does not confer lifelong immunity