Pertussis (Whooping Cough)

Clinical assessment

Clinical suspicion based on characteristic cough (paroxysmal, whoop, post-tussive vomiting) lasting ≥2 weeks, especially during an outbreak or with known exposure. Diagnosis often made clinically. Differential diagnosis: Other causes of prolonged cough (viral bronchitis, Mycoplasma/Chlamydia pneumonia, asthma, GERD, foreign body, TB), Croup (barking cough, stridor), Bronchiolitis (wheeze, younger infants).

Investigations

• Nasopharyngeal Swab/Aspirate:
• - Culture for Bordetella pertussis: Gold standard but sensitivity decreases after first 2 weeks of cough and after antibiotics. Requires specific media.
• - PCR for B. pertussis DNA: Highly sensitive and specific, preferred method, useful up to 3-4 weeks after cough onset.
• Blood: Complete Blood Count (CBC) may show marked lymphocytosis (high lymphocyte count), especially in infants/young children.
• Serology (Antibody testing): Useful later in illness (>2-3 weeks cough), requires paired sera or specific IgM/IgA interpretation. Less useful for acute diagnosis.
• Chest X-ray: Usually normal or may show peribronchial thickening; used to exclude pneumonia.

Diagnostic criteria

Clinical diagnosis based on characteristic cough illness ≥2 weeks, OR laboratory confirmation (positive culture or PCR).

Non-pharmacological management

• Supportive Care:
• - Maintain hydration and nutrition (small, frequent feeds may be better tolerated).
• - Gentle suctioning of secretions if needed.
• - Oxygen therapy if hypoxic.
• - Minimize stimuli that trigger coughing paroxysms.
• Hospitalization: Required for infants (<3-6 months), severe cases with apnea/cyanosis/pneumonia/seizures, or inability to feed.
• Infection Control:
• - Droplet precautions for hospitalized patients until 5 days of effective antibiotic therapy completed.
• - Exclude cases from school/daycare until 5 days of antibiotics completed.
• - Reportable disease.

Pharmacological treatment

• Antibiotics: Primarily given to reduce infectivity (limit spread) and may shorten duration/severity if started early (within first 1-2 weeks of cough - catarrhal/early paroxysmal phase). Less effective if started later but still recommended to decrease transmission.
• - Macrolides are preferred:
• - Azithromycin: Child <6mo: 10mg/kg/day OD x 5 days. Child ≥6mo: 10mg/kg (max 500mg) OD on Day 1, then 5mg/kg (max 250mg) OD on Days 2-5. Adult: 500mg OD Day 1, then 250mg OD Days 2-5.
• - Erythromycin: 40-50 mg/kg/day divided QID (Adult 500mg QID) for 7-14 days (UCG 2023 specifically mentions 7 days). (More side effects, longer course).
• - Clarithromycin: Alternative macrolide.
• - Alternative if macrolide allergic/intolerant: Trimethoprim-Sulfamethoxazole (TMP-SMX) - Contraindicated in infants <2 months.
• Cough suppressants, antihistamines, mucolytics: NOT effective and NOT recommended.
• Corticosteroids: No proven benefit.

Monitoring

• Monitor respiratory status (frequency/severity of paroxysms, apnea, cyanosis).
• Monitor feeding and hydration.
• Monitor for complications (pneumonia, seizures).