Key Facts

Pertussis remains an important cause of morbidity and mortality in young infants despite vaccination. The UK maternal vaccination programme, introduced in 2012 following a major outbreak, has been highly effective in reducing neonatal disease.

Epidemiology

Pertussis notifications in England: typically 5,000-10,000 per year with cyclical peaks every 3-4 years. Incidence is highest in infants <3 months (too young to be vaccinated). ~90% of pertussis deaths occur in infants <3 months. Adolescents and adults are an important reservoir of infection (waning immunity).

Aetiology

• Bordetella pertussis: Primary pathogen
• Bordetella parapertussis: Milder illness; not prevented by pertussis vaccine
• Transmission: Respiratory droplets; highly contagious; incubation 7-21 days

Pathophysiology

B. pertussis attaches to ciliated respiratory epithelium via filamentous haemagglutinin and pertactin. It produces pertussis toxin (ADP-ribosylating exotoxin) which impairs immune cell function, increases insulin secretion (causing lymphocytosis), and sensitises the cough reflex. Tracheal cytotoxin causes ciliated cell damage and mucus hypersecretion. The paroxysmal cough is mediated by sensitisation of cough receptors and persists for weeks after the organism is cleared.

Three Phases

Catarrhal phase (1-2 weeks):

• Coryzal symptoms, mild cough, low-grade fever
• MOST INFECTIOUS period

Paroxysmal phase (2-8 weeks):

• Paroxysms of intense cough (10-30 coughs in a row)
• Inspiratory 'whoop' between paroxysms
• Post-tussive vomiting
• Facial congestion/cyanosis during paroxysms
• May be well between paroxysms

Convalescent phase (weeks to months):

• Gradual resolution; cough may persist for months ('100-day cough')
• Paroxysms may recur with subsequent viral infections

Infants <3 Months

• May NOT whoop — too small to generate whoop
• Apnoea may be the ONLY feature
• Cyanotic episodes, feeding difficulty
• High risk of complications: Pneumonia, seizures, encephalopathy, death

Red Flags

• Apnoea in young infant — admit for monitoring
• Marked lymphocytosis (>20 × 10⁹/L) with leucocytosis — correlates with severe disease in infants
• Pulmonary hypertension — rare but can be fatal in infants with hyperleucocytosis

Bedside

• SpO2: During paroxysms
• Video of paroxysm: Helpful if not witnessed by clinician

Bloods

• FBC: Marked lymphocytosis (>10 × 10⁹/L in >50% of cases; >20 correlates with severity)
• Anti-pertussis toxin IgG: Oral fluid or serum — diagnostic after 2 weeks of symptoms

Microbiology

• Nasal swab PCR: Best in first 2-3 weeks; specificity >95%
• Culture: Gold standard but slow (takes 7 days); sensitivity lower than PCR

Imaging

• CXR: If pneumonia suspected; may show perihilar infiltrates or consolidation

Pharmacological

• Azithromycin: 10mg/kg OD for 3 days (first-line) — reduces infectivity; does NOT shorten paroxysmal phase if already established
• Clarithromycin: Alternative (7.5mg/kg BD for 7 days)
• Most effective if given during catarrhal phase
• Antibiotics for household contacts (post-exposure prophylaxis) — especially if vulnerable contacts (pregnant women, young infants)

Non-pharmacological

• Admission: Infants <6 months (especially <3 months); apnoeas; severe paroxysms; feeding difficulty
• Monitoring: Continuous SpO2 and apnoea monitoring for young infants
• Supportive care: Small frequent feeds, minimal stimulation, oxygen if needed
• Suction: Gentle nasal suction if needed

Prevention

• Childhood vaccination: 6-in-1 (DTaP) at 8, 12, 16 weeks + pre-school booster at 3yr 4mo
• Maternal vaccination: Pertussis-containing vaccine (dTaP/IPV) from 16 weeks gestation — ~90% effective at preventing infant disease
• Post-exposure prophylaxis: Azithromycin for household contacts
• School exclusion: 48 hours after starting antibiotics or 21 days from symptom onset if untreated

Referral Criteria

• All infants <3 months with suspected pertussis — admission
• Apnoeas or cyanotic episodes — PICU assessment
• Severe lymphocytosis in infant — haematology/PICU (exchange transfusion in extreme cases)

• Overall mortality: <0.5% in developed countries; higher in unvaccinated infants <3 months
• Infant mortality: ~1% in hospitalised infants <3 months; most deaths from pulmonary hypertension/hyperleucocytosis
• Duration: Paroxysmal cough lasts 2-8 weeks; total illness 6-12 weeks ('100-day cough')
• Post-pertussis bronchiectasis: Rare with modern management
• Maternal vaccination: Has reduced infant pertussis deaths by ~90% since introduction

Pertussis Phases

When to Notify and Test