Bordetella pertussis
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Pertussis key Points
- Epidemics typically occur every 3-5 years
- Paroxysmal cough that can induce vomiting, cough apnoea and raised ICP are features of infection
- Bordatella have fimbriae that aid adhesion and produce exotoxins
- Diagnosis is typically via pernasal nasopharynx swab or if symptoms present > 2 weeks via serology
- May last for two or three months hence 'the 100-day cough'
- Antibiotics do not alter the clinical course once the disease is established. Macrolide antibiotics may curtail the period of infectivity (should not be given if symptoms present >3 weeks as patients considered non-infectious three weeks after onset of symptom)
Background
Bordetella Pertussis, is a Gram-negative, aerobic coccobacillus, that causes whooping cough.Pathophysiology
Bordetella Pertussis infects the respiratory tract, adhering to ciliated epithelial cells and releasing toxins that disrupt normal respiratory function. Key virulence factors include:- Adhesins (e.g. filamentous haemagglutinin, pertactin, fimbriae) that facilitate attachment to the respiratory epithelium
- Toxins: pertussis toxin (PT), adenylate cyclase toxin, and tracheal cytotoxin contribute to local tissue damage and systemic effects. Pertussis toxin disrupts immune signalling, leading to lymphocytosis, adenylate cyclase toxin impairs phagocyte function whilst tracheal cytotoxin damages ciliated cells, impairing mucociliary clearance.
Epidemiology in the UK
Pertussis typically exhibits cyclical outbreaks every 3 to 5 years in the UK with major outbreaks in 2012, 2016 and 2024 (the COVID-19 pandemic is likely to have interrupted the normal cycle timing). In epidemic years UK cases will often rise to over 10,000 cases and are usually associated with >10 infant deaths.Infants under 3 months are at highest risk due to incomplete vaccination. Uptake of maternal vaccination has declined in recent years, from 71% in 2020 to 61% in 2023.
Transmission
Transmission occurs primarily via respiratory droplets from coughing or sneezing.Incubation period
Incubation period is typically 7–10 days, but can extend up to 21 daysIndividuals are most infectious during the early catarrhal and initial paroxysmal phases (the first 3 weeks of infection).
Clinical Features
Pertussis progresses through three distinct clinical stages:- Catarrhal phase (1–2 weeks): non-specific symptoms including mild cough, rhinorrhoea, and low-grade fever
- Paroxysmal phase (1–6 weeks): severe paroxysmal coughing fits followed by inspiratory whoop (whooping often absent in adults), gasping, post-tussive vomiting, and/or fatigue.
- Convalescent phase (weeks to months): gradual resolution of symptoms, though cough may persist
Complications
Pertussis can lead to serious complications, especially in young infants. These include:
- Apnoea (in approximately 68% of hospitalised infants under 1 year)
- Pneumonia (22% of cases, often due to secondary bacterial infection)
- Seizures (1 in 50)
- Encephalopathy (1 in 150)
Summary of the diagnostic methods for whooping cough:
| Diagnostic method | Age, timing | notes | |
|---|---|---|---|
| Polymerase chain reaction (PCR) | Infants or early in illness | High sensitivity, useful in first 3 weeks | |
| Culture | Neonates and infants | Most specific test but lower sensitivity, ideally within 2 weeks of cough onset | |
| Serology (anti-pertussis toxin IgG) | ≥2 weeks after symptom onset in older children or adults | Used when PCR or culture not possible or negative | |
| Clinical diagnosis | All ages | Made on characteristic symptoms if tests are unavailable or negative |
UK Vaccination Schedule
The UK immunisation programme includes pertussis vaccination as follows:
- Routine infant schedule: part of the 6-in-1 vaccine given at 8, 12, and 16 weeks of age and the 4-in-1 pre-school booster given at around 3 years and 4 months.
- Maternal vaccination: a single dose of the pertussis-containing vaccine between 16 and 32 weeks of pregnancy
Management
Management includes both antimicrobial and supportive strategies:
- Admission should be arranged for those with significant breathing difficulty (e.g. apnoea episodes, severe paroxysms, or cyanosis) and a low threshold used for admitting children aged 6 months or younger.
- Antibiotics: macrolides (such as azithromycin or clarithromycin) are most effective if administered during the catarrhal phase. Later administration does not significantly alter illness duration but helps prevent transmission. Antibiotics are indicated if prescribed within 14 days from the onset of coughing and should be considered within 21 days from the onset of coughing to reduce further transmission.
- Supportive care: may include hospitalisation in severe cases, particularly in infants, with attention to respiratory support, fluid management, and monitoring for complications