Overview
Pertussis
1. Clinical Overview
Summary
Pertussis (whooping cough) is a highly contagious acute respiratory tract infection caused by the bacterium Bordetella pertussis. It is characterised by severe, spasmodic coughing episodes typically followed by an inspiratory "whoop" and post-tussive vomiting. While it can affect all ages, it is most dangerous in infants under 6 months, who are at high risk of apnoea, pneumonia, and death. Management primarily involves supportive care and early antibiotics (macrolides) to reduce transmission. Prevention through vaccination (including maternal vaccination) is critical. [1,2]
Key Facts
- Causative Agent: Bordetella pertussis (Gram-negative coccobacillus).
- Infectivity: Highly contagious (R₀ 12-17); attack rate 80-90% in non-immune contacts.
- Classic Stages: Catarrhal (1-2 weeks), Paroxysmal (1-6 weeks), Convalescent (weeks-months).
- "100 Day Cough": Symptoms can persist for months after infection clearance.
- Infant Risk: Infants less than 3 months often do NOT whoop; presenting instead with apnoea or cyanosis.
- Treatment: Macrolides (Azithromycin/Clarithromycin) clear bacteria but only alter course if started in Catarrhal phase.
- Prevention: DTaP vaccine; maternal vaccination (20-32 weeks) confers passive immunity to neonates.
Clinical Pearls
The "Silent" Infant: Young infants often lack the characteristic "whoop." Their primary presentation may be apnoea, bradycardia, or cyanosis without a prominent cough. Have a low threshold for admitting young infants.
Lymphocytosis is Key: A very high lymphocyte count (e.g., >20-30 x 10⁹/L) in an afebrile infant with a cough is highly suggestive of pertussis. The degree of lymphocytosis correlates with mortality risk (hyperviscosity).
School Exclusion: Exclude from school/nursery for 48 hours after starting antibiotics, or for 21 days from onset of symptoms if untreated.
Vaccination in Pregnancy: The most effective way to protect preventing infant death is maternal vaccination. This provides transplacental IgG transfer, protecting the infant before their first primary immunisations at 8 weeks.
2. Epidemiology
Incidence
- Cyclical: Epidemics occur every 3-5 years despite high vaccination coverage.
- Resurgence: Increasing cases globally due to waning immunity and better detection.
- Age Distribution: Bimodal - peak in infants less than 6 months (severe disease) and adolescents/adults (often milder/missed).
Transmission
- Route: Respiratory droplets (coughing, sneezing).
- Incubation Period: 7-10 days (range 5-21 days).
- Infectious Period: From onset of catarrhal symptoms until 21 days after cough onset (or 48 hours after effective antibiotics).
Risk Groups for Severe Disease
- Infants less than 6 months: Highest mortality and complication rate.
- Unvaccinated children: No immunity.
- Premature infants: Underlying lung vulnerability.
- Cardiopulmonary comorbidities: Increased risk of decompensation.
3. Pathophysiology
Step 1: Attachment and Evasion
- B. pertussis binds to ciliated respiratory epithelium via filamentous haemagglutinin (FHA) and pertactin.
- Evades immune clearance (paralyzes cilia).
Step 2: Toxin Production
- Pertussis Toxin (PT):
- Systemic effects: Causes lymphocytosis (blocks lymphocyte extravasation).
- Insulin secretion: Can cause hypoglycaemia.
- Immune modulation: Inhibits phagocyte migration.
- Tracheal Cytotoxin (TCT):
- Destroys ciliated epithelial cells.
- Paralyses mucociliary escalator → accumulation of secretions → severe cough.
- Adenylate Cyclase Toxin: Inhibits phagocytosis.
Step 3: Local Inflammation
- Necrosis of respiratory epithelium.
- Inflammation and mucous hypersecretion in small airways.
- Airway obstruction, micro-atelectasis, and V/Q mismatch (hypoxia).
Step 4: Systemic Effects (Severe Pertussis)
- Leukocytosis: Extreme lymphocytosis can lead to leukostasis and pulmonary hypertension.
- Encephalopathy: Likely due to hypoxia, intracranial haemorrhage, or toxin effects.
Step 5: Resolution
- Slow regeneration of ciliated epithelium (takes weeks to months).
- Explains the prolonged "convalescent" coughing phase.
4. Clinical Presentation
Clinical Course: The Three Stages
| Stage | Duration | Symptoms |
|---|---|---|
| 1. Catarrhal | 1-2 weeks | Coryza, mild fever, sneezing, mild cough (indistinguishable from viral URI). Most infectious stage. |
| 2. Paroxysmal | 1-6 weeks | Severe coughing fits, inspiratory "whoop", post-tussive vomit, cyanosis, apnoea. Worse at night. |
| 3. Convalescent | 2-3 months | Gradual reduction in cough. Paroxysms may recur with viral URIs. |
Symptoms by Age
Infants (less than 6 months)
Children
Adolescents/Adults
Red Flags - "The Don't Miss" Signs
- Apnoea (especially in infants).
- Severe tachycardia (>160-180 bpm) + respiratory distress (malignant pertussis).
- Leucocytosis (>50 x 10⁹/L) predicts pulmonary hypertension/death.
- Seizures or altered conscious state.
- Significant dehydration from post-tussive vomiting.
Paroxysms
May not be classic.
Whoop
Often absent (inspiratory muscle weakness).
Apnoea
Common presentation.
Feeding
Poor feeding, vomiting, dehydration.
Seizures
Due to hypoxia.
5. Clinical Examination
Between Paroxysms (Inter-ictal)
- Child may look surprisingly well/normal.
- No fever (usually).
- Chest often clear on auscultation (unless secondary pneumonia).
During Paroxysm
- Intense, repetitive coughing (5-10 coughs in one expiration).
- Tongue protrusion.
- Facial plethora / cyanosis.
- Distended neck veins.
- Inspiratory "Whoop" (stridor-like sound of forced inspiration against narrowed glottis).
- Vomiting mucus or food.
Specific Signs
- Subconjunctival haemorrhages: Due to raised intrathoracic pressure.
- Petechiae: Face and upper torso.
- Frenutal Ulcer: Ulcer under tongue from friction against lower teeth during cough.
- Dehydration: Dry mucous membranes, sunken fontanelle.
6. Investigations
Diagnosis
Microbiology (Gold Standard)
| Test | Sample | Sensitivity | Utility |
|---|---|---|---|
| PCR | Nasopharyngeal swab/aspirate | High (up to 4 weeks) | Test of choice |
| Culture | Nasopharyngeal swab (pernasal) | Low (less than 60%) | Takes 3-7 days; 100% specific |
| Serology | Blood (Anti-PT IgG) | High (late disease) | Use if >2-3 weeks from onset |
When to test?
- less than 2 weeks: PCR.
- 2-4 weeks: PCR and Serology.
- >4 weeks: Serology only.
Supportive Investigations
Full Blood Count (FBC)
- Lymphocytosis: Key finding. WCC often >20, up to 100 x 10⁹/L.
- Prognostic Marker: WCC >50-100 correlates with "malignant pertussis" (pulmonary hypertension, high mortality).
Chest X-Ray
- Often normal.
- "Shaggy heart" border (peribronchial thickening).
- Atelectasis.
- Consolidation (secondary pneumonia).
Blood Gas
- If severe respiratory distress/apnoea.
- Hypoxia, hypercarbia (exhaustion).
7. Management
Management Algorithm
SUSPECTED PERTUSSIS
(Cough >2 weeks OR Paroxysms/Whoop/Vomit)
↓
┌─────────────────────────────────────────────┐
│ ASSESS SEVERITY │
│ - Age (less than 6 months = High Risk) │
│ - Apnoea / Cyanosis │
│ - Feeding / Hydration │
└─────────────────────────────────────────────┘
↓
┌───────────┴───────────┐
↓ ↓
SEVERE / HIGH RISK MILD / LOW RISK
(Infants less than 6mo, Apnoea) (Older child, stable)
↓ ↓
ADMIT TO HOSPITAL MANAGE AT HOME
↓ ↓
┌─────────────────────┐ ┌─────────────────────┐
│ - Isolation (Droplet)│ │ - Antibiotics (if │
│ - O2 / Resp Support │ │ less than 21 days onset) │
│ - Antibiotics │ │ - Isolation │
│ - IV Fluids │ │ - Safety netting │
│ - Monitor Lymphocytes│ │ - Notify P.H. │
└─────────────────────┘ └─────────────────────┘
↓
If WCC >50 or
Severe Failure
↓
PICU ADMISSION
(Exchange transfusion
/ ECMO considered)
Antimicrobial Therapy
Rationale:
- Reduces transmission (eradicates organism from nasopharynx).
- Does NOT reduce symptoms (unless started in early Catarrhal stage).
- Indicated if onset of cough is within 21 days.
Regimens:
| Drug | Age Group | Dose | Duration | Notes |
|---|---|---|---|---|
| Azithromycin | less than 6 months | 10mg/kg OD | 5 days | Preferred in neonates |
| Azithromycin | >6 months | 10mg/kg Day 1; 5mg/kg Day 2-5 | 5 days | Better compliance |
| Clarithromycin | All ages | Age-based dosing BD | 7 days | Alternative |
| Erythromycin | All ages | QDS dosing | 14 days | GI side effects common |
| Co-trimoxazole | >6 weeks | BD dosing | 14 days | Second line (macrolide allergy) |
Contraindication caution: Macrolides in neonates (less than 2 weeks) associated with Pyloric Stenosis (monitor for vomiting). However, benefit usually outweighs risk in pertussis.
Supportive Inpatient Care
- Monitoring: Oxygen saturations, heart rate (apnoea monitoring essential).
- Respiratory Support:
- Oxygen (if hypoxic).
- Suction (clear secretions post-vomit).
- HFNC / CPAP (for apnoea/distress).
- Intubation/Ventilation (for exhaustion/failure).
- Fluid & Nutrition:
- NG feeding or IV fluids (if frequent vomiting preventing oral intake).
- Small frequent feeds.
- Avoid over-hydration (SIADH risk).
Management of "Malignant Pertussis"
- Criteria: Young infant, WCC >50-100, severe pneumonia/pulmonary hypertension/shock.
- Intervention: Exchange Transfusion or Leukapheresis (to reduce WBC mass and hyperviscosity).
- ECMO: May be required for refractory hypoxaemia/pulmonary hypertension.
- Steroids: Not routinely recommended.
Public Health
- Notifiable Disease: Report to public health authorities.
- Isolation: Droplet precautions until 5 days of effective antibiotics completed (or 21 days if untreated).
- Contact Prophylaxis: Antibiotics for high-risk household contacts (e.g., infants, pregnant women) regardless of vaccination status.
8. Complications
Respiratory
- Apnoea: Commonest cause of death in infants.
- Pneumonia: Primary (pertussis) or Secondary bacterial (Pneumococcus, S. aureus).
- Pulmonary Hypertension: Due to leukocyte aggregates (malignant pertussis).
- Atelectasis: Mucus plugging.
- Pneumothorax / Pneumomediastinum: From force of coughing.
Neurological
- Seizures: Hypoxia or toxin-mediated.
- Encephalopathy: Rare, permanent damage possible.
- Intracranial Haemorrhage: Subdural/subarachnoid from venous pressure during cough.
Nutritional/Mechanical
- Weight loss: Vomiting.
- Hernias: Inguinal/umbilical (from intra-abdominal pressure).
- Rib fractures.
- Frenutal ulcer.
9. Prognosis and Outcomes
Mortality
- Overall: Low (less than 1%).
- Infants less than 2 months: Death rate ~1% (highest risk group).
- Adults: Rare mortality.
Recovery
- Cough: Persists for months ("100 day cough").
- Recurrence: Paroxysms can be triggered by future viral URIs for up to a year.
- Long-term: Some association with bronchiectasis or chronic cough.
10. Evidence and Guidelines
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| NICE CKS | UK | Antibiotics within 21 days; admission criteria |
| PHE Guidelines | UK | Public health management; prophylaxis |
| AAP Red Book | USA | Diagnostic criteria and treatment |
Landmark Studies
1. Maternal Vaccination Efficacy (Amirthalingam et al. 2014) [4]
- Finding: Vaccination in pregnancy provides 91% vaccine effectiveness against infant pertussis.
- Impact: Shifted global strategy to prioritize maternal immunization.
2. Altunaiji et al. Antibiotics for Pertussis (Cochrane 2007) [5]
- Finding: Antibiotics eradicate organism but do not shorten symptom duration unless started in catarrhal stage.
- Impact: Defined limited window for therapeutic benefit.
3. Malignant Pertussis & Hyperleukocytosis (Paddock et al. 2008)
- Finding: Correlation between extreme lymphocytosis, pulmonary hypertension, and death.
- Impact: Basis for exchange transfusion therapy.
11. Patient and Layperson Explanation
What is Whooping Cough?
Whooping cough (pertussis) is a bacterial infection of the lungs. It is called the "100 day cough" because it lasts a very long time.
Why is it dangerous?
For older children and adults, it is usually just a nasty, annoying cough. However, for babies under 6 months, it can be life-threatening. They may stop breathing (apnoea) or turn blue instead of coughing.
What are the symptoms?
- Stage 1 (Cold-like): Runny nose, mild fever. This lasts 1-2 weeks. This is when it is most catching.
- Stage 2 (Coughing fits): Violent bursts of rapid coughing. You can't catch a breath. At the end, you may make a "whoop" noise gasping for air. You might vomit afterwards.
- Stage 3 (Recovery): Cough slowly gets better but can last months.
How is it treated?
- Antibiotics: These kill the bacteria so you stop being contagious. They only stop the cough if started very early (in the first week or two).
- Hospital: Babies often need to stay in hospital to have their breathing and oxygen monitored.
Can it be prevented?
Yes.
- Vaccination: Part of the standard "6-in-1" baby jabs (at 8, 12, 16 weeks) and pre-school booster.
- Pregnancy: Pregnant women are vaccinated (usually 20-32 weeks) to pass protection to their baby for those first vulnerable weeks of life.
When to seek help?
- If your baby stops breathing or turns blue.
- If coughing fits are severe and causing vomiting.
- If a baby under 6 months seems unwell or is feeding poorly.
12. References
Primary Sources
- Kilgore PE, et al. Pertussis: Microbiology, Disease, Treatment, and Prevention. Clin Microbiol Rev. 2016;29:449-486. PMID: 27281741.
- Cherry JD. Pertussis in young infants. Arch Dis Child. 2013;98:1-2.
- NICE Clinical Knowledge Summaries. Whooping cough. https://cks.nice.org.uk/topics/whooping-cough/. Accessed 2025.
- Amirthalingam G, et al. Effectiveness of maternal pertussis vaccination in England: an observational study. Lancet. 2014;384:1521-1528. PMID: 25035028.
- Altunaiji SM, et al. Antibiotics for whooping cough (pertussis). Cochrane Database Syst Rev. 2007;CD004404. PMID: 17636756.
- Public Health England. Pertussis (whooping cough): guidelines for public health management. 2018.
13. Examination Focus
Common Exam Questions
- Paediatrics: "A 6-week-old infant presents with apnoea and poor feeding. WCC is 35. Diagnosis?"
- Answer: Pertussis. (Classic presentation in infants: apnoea without whoop + lymphocytosis).
- Public Health: "A child is diagnosed with pertussis. When can they return to school?"
- Answer: 48 hours after starting appropriate antibiotics, or 21 days from onset if untreated.
- Obstetrics/GP: "Why vaccinate in pregnancy?"
- Answer: Passive transplacental transfer of IgG protects the infant in the first 2 months before their own primary immunisations.
- Pharmacology: "Antibiotic of choice?"
- Answer: Macrolide (Clarithromycin/Azithromycin). Note risk of pyloric stenosis in neonates but benefit usually outweighs risk.
Viva Points
- Lymphocytosis: Why? Pertussis toxin prevents lymphocytes leaving blood to enter lymph nodes.
- Hyper-viscosity: Extreme WCC leads to pulmonary hypertension and death (Malignant Pertussis).
- Diagnosis: PCR is superior to culture (slow) and serology (only good for late disease).
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