Pertussis (B. pertussis and parapertussis) in Children

Introduction to Pertussis in Children

Pertussis, also known as whooping cough, is a highly contagious respiratory disease primarily caused by the bacterium Bordetella pertussis. Less commonly, it can be caused by Bordetella parapertussis. Pertussis remains a significant public health concern, particularly for infants and young children, despite widespread vaccination efforts.

Key Points:

Caused primarily by Bordetella pertussis, a gram-negative coccobacillus
Transmission occurs through respiratory droplets
Characterized by paroxysmal coughing fits, often followed by a distinctive "whooping" sound
Most severe in infants, especially those under 6 months of age
Can occur in vaccinated individuals, but usually with milder symptoms
B. parapertussis causes a similar but typically milder illness

Understanding the clinical features, diagnosis, and management of pertussis is crucial for healthcare providers, as early recognition and treatment can significantly impact disease course and prevent complications, especially in young children.

Epidemiology of Pertussis

Global Burden:

Worldwide, an estimated 24.1 million cases and 160,700 deaths in children <5 years (WHO, 2014)
Resurgence noted in several countries despite high vaccination coverage

Age Distribution:

Highest incidence and mortality in infants <1 year, especially <6 months
Increasing incidence in adolescents and adults, who serve as reservoirs

Transmission:

Highly contagious: attack rates up to 90% in susceptible household contacts
Spread through respiratory droplets or direct contact with respiratory secretions
Most infectious during catarrhal and early paroxysmal stages

Seasonal Variation:

Peak incidence typically in late summer and early fall in temperate climates
Can occur year-round, with outbreaks possible at any time

Vaccine Impact:

Significant reduction in incidence and mortality since introduction of vaccines
Shift in age distribution towards adolescents and adults due to waning immunity
Emergence of vaccine-escape strains reported in some regions

Pathogenesis of Pertussis

Bacterial Factors:

Adhesins:
- Filamentous hemagglutinin (FHA)
- Pertactin (PRN)
- Fimbriae (FIM)
Toxins:
- Pertussis toxin (PT): Key virulence factor, causes lymphocytosis
- Adenylate cyclase toxin (ACT): Impairs neutrophil function
- Tracheal cytotoxin (TCT): Damages respiratory epithelium

Stages of Infection:

Attachment: Adhesins facilitate binding to ciliated respiratory epithelial cells
Evasion of host defenses: Toxins impair immune response
Local damage: Ciliary paralysis and epithelial damage
Systemic effects: PT-induced lymphocytosis and other systemic manifestations

Host Immune Response:

Initially dominated by innate immune responses
Adaptive immunity develops, with both humoral and cell-mediated components
Immunity after natural infection wanes over time (5-10 years)

Factors Influencing Severity:

Age: Most severe in young infants due to immature immune systems
Vaccination status: Vaccinated individuals typically have milder disease
Comorbidities: Underlying conditions may increase risk of severe disease

Clinical Presentation of Pertussis

Classic Stages:

Catarrhal Stage (1-2 weeks):
- Mild upper respiratory symptoms (rhinorrhea, low-grade fever)
- Gradual onset of cough
- Highly contagious during this stage
Paroxysmal Stage (2-6 weeks):
- Characteristic paroxysmal coughing fits
- Post-tussive vomiting
- Inspiratory "whoop" in some cases
- Cyanosis or apnea, especially in infants
Convalescent Stage (weeks to months):
- Gradual resolution of symptoms
- Persistent cough may last for weeks to months

Age-Specific Presentations:

Infants (<6 months):
- May not exhibit classic "whoop"
- Apnea, cyanosis, and feeding difficulties more common
- Higher risk of severe complications
Older Children and Adolescents:
- May have milder symptoms, especially if vaccinated
- Prolonged cough often the primary symptom

Atypical Presentations:

Vaccinated individuals may have milder, nonspecific symptoms
Consider pertussis in any prolonged cough illness, especially if paroxysmal

Diagnosis of Pertussis

Clinical Diagnosis:

Based on characteristic cough and associated symptoms
World Health Organization (WHO) clinical case definition:
- Cough lasting ≥2 weeks with at least one of:
  - Paroxysms of coughing
  - Inspiratory "whoop"
  - Post-tussive vomiting

Laboratory Diagnosis:

Polymerase Chain Reaction (PCR):
- Most sensitive and specific method
- Rapid results (within 24-48 hours)
- Can detect non-viable organisms
Culture:
- Gold standard, but less sensitive than PCR
- Requires special media (Regan-Lowe or Bordet-Gengou)
- Results take 7-10 days
Serology:
- Useful in later stages of illness
- Single high anti-PT IgG titer or significant rise in titer
- Limited utility in vaccinated individuals

Other Investigations:

Complete Blood Count: May show characteristic lymphocytosis
Chest X-ray: Often normal, may show perihilar infiltrates or atelectasis

Differential Diagnosis:

Other causes of prolonged cough: Mycoplasma, Chlamydophila, viral infections
Cystic fibrosis
Foreign body aspiration
Asthma or reactive airway disease

Treatment of Pertussis

Antimicrobial Therapy:

Primary goals: Reduce transmission and modify course if given early
Recommended antibiotics:
- Azithromycin: First-line for all ages
  - <6 months: 10 mg/kg once daily for 5 days
  - ≥6 months: 10 mg/kg (max 500 mg) on day 1, then 5 mg/kg (max 250 mg) on days 2-5
- Clarithromycin: Alternative for ≥1 month old
  - 15 mg/kg/day in 2 divided doses (max 1 g/day) for 7 days
- Trimethoprim-sulfamethoxazole: Alternative for ≥2 months old
  - 8 mg/kg/day trimethoprim, 40 mg/kg/day sulfamethoxazole in 2 doses for 14 days

Supportive Care:

Hospitalization often required for infants <6 months or those with severe disease
Oxygen therapy and suctioning as needed
Maintain hydration and nutrition
Monitor for apnea, especially in young infants

Management of Complications:

Pneumonia: Additional antibiotics if bacterial superinfection suspected
Seizures: Anticonvulsant therapy as indicated
Respiratory failure: May require mechanical ventilation

Additional Considerations:

Avoid antitussives (ineffective and potentially harmful)
Corticosteroids: Not routinely recommended, may be considered in severe cases
Close monitoring of infants, especially those <6 months

Complications of Pertussis

Respiratory Complications:

Pneumonia: Most common severe complication
- Can be primary (due to B. pertussis) or secondary bacterial infection
- Occurs in up to 20% of infants <6 months
Atelectasis
Pneumothorax or pneumomediastinum (rare)
Respiratory failure requiring mechanical ventilation

Neurologic Complications:

Seizures: Due to hypoxia or pertussis encephalopathy
Encephalopathy: Rare but serious
- May lead to long-term neurological sequelae
- Exact mechanism unclear (hypoxia, toxin effect, or hemorrhage)
Intracranial hemorrhage: From increased intracranial pressure during coughing

Other Complications:

Nutritional: Weight loss, dehydration
Musculoskeletal: Rib fractures (rare, usually in adults)
Urinary incontinence
Subconjunctival hemorrhage
Umbilical or inguinal hernia

Long-term Sequelae:

Persistent cough (for weeks to months)
Decreased lung function (usually transient)
Neurological sequelae in cases of severe encephalopathy

Mortality:

Highest in infants <6 months
Main causes: Pneumonia, refractory pulmonary hypertension, cardiac failure

Prevention of Pertussis

Vaccination:

Primary prevention strategy
Types of vaccines:
- DTaP (Diphtheria, Tetanus, acellular Pertussis): For children <7 years
- Tdap (Tetanus, diphtheria, acellular pertussis): For adolescents and adults
Recommended schedule (USA):
- DTaP: 5-dose series at 2, 4, 6, 15-18 months, and 4-6 years
- Tdap: Single dose at 11-12 years
- Pregnant women: Tdap with each pregnancy (preferably at 27-36 weeks gestation)
Vaccine efficacy:
- ~80-90% after 3-dose primary series
- Waning immunity over time, especially with acellular vaccines

Chemoprophylaxis:

Recommended for high-risk close contacts of pertussis cases
Same antibiotics and dosing as treatment
Prioritize:
- Household contacts
- Infants and their household members
- Pregnant women in their third trimester
- Individuals with pre-existing health conditions at risk for severe illness

Infection Control Measures:

Droplet precautions for hospitalized patients
Exclusion from school/childcare until 5 days of appropriate antibiotic therapy completed
Encourage good respiratory hygiene and hand washing

Public Health Strategies:

Surveillance and rapid case identification
Contact tracing and management
Education of healthcare providers and the public
Promotion of vaccination, including "cocooning" strategy (vaccinating close contacts of infants)

Bordetella parapertussis Infections

Overview:

Causes a pertussis-like illness, generally milder than B. pertussis
Accounts for 5-20% of pertussis-like infections in some populations

Key Differences from B. pertussis:

Does not produce pertussis toxin
Often shorter duration of illness
Less likely to cause severe complications

Clinical Presentation:

Similar to B. pertussis but typically milder
May be indistinguishable from pertussis in some cases
Paroxysmal cough and post-tussive vomiting can occur

Diagnosis:

PCR: Can differentiate B. parapertussis from B. pertussis
Culture: Grows on standard Bordetella media
Serology: Limited utility due to cross-reactivity with B. pertussis

Treatment:

Similar to B. pertussis
Macrolides (azithromycin, clarithromycin) are first-line
Supportive care as needed

Prevention:

Current pertussis vaccines do not provide protection against B. parapertussis
Similar infection control measures as for B. pertussis

Public Health Implications:

May be underdiagnosed due to milder presentation
Can circulate in highly vaccinated populations
Importance of species-specific diagnosis for accurate epidemiological data

Objective QnA: Pertussis (B. pertussis and parapertussis) in Children

Question: What is the causative agent of pertussis? Answer: Bordetella pertussis and, less commonly, Bordetella parapertussis
Question: What is the typical incubation period for pertussis? Answer: 7-10 days, with a range of 5-21 days
Question: What are the three classic stages of pertussis? Answer: Catarrhal stage, paroxysmal stage, and convalescent stage
Question: What is the characteristic sound associated with pertussis cough? Answer: Inspiratory "whoop"
Question: In which age group is pertussis most severe and potentially fatal? Answer: Infants under 6 months of age
Question: What is the recommended method for diagnosing pertussis in the first 2-3 weeks of illness? Answer: PCR testing of nasopharyngeal specimens
Question: What is the first-line antibiotic treatment for pertussis in children? Answer: Azithromycin
Question: How long is the typical duration of the paroxysmal stage in pertussis? Answer: 1-6 weeks, sometimes longer
Question: What is the most common complication of pertussis in infants? Answer: Pneumonia
Question: What is the recommended post-exposure prophylaxis for household contacts of pertussis cases? Answer: Antibiotic treatment, regardless of vaccination status
Question: What is the composition of the DTaP vaccine? Answer: Diphtheria toxoid, tetanus toxoid, and acellular pertussis antigens
Question: At what ages are DTaP vaccines recommended in the primary series? Answer: 2 months, 4 months, 6 months, 15-18 months, and 4-6 years
Question: What is the difference between DTaP and Tdap vaccines? Answer: DTaP is for children under 7, while Tdap is for adolescents and adults
Question: Why is cocooning recommended for pertussis prevention in infants? Answer: To protect infants by vaccinating close contacts who might transmit the disease
Question: What percentage of vaccinated children may still get pertussis if exposed? Answer: Approximately 10-20%
Question: What is the recommended management for apnea in infants with pertussis? Answer: Hospitalization and close monitoring
Question: How long can pertussis bacteria persist in the nasopharynx after infection? Answer: Up to 6 weeks after onset of symptoms
Question: What is the role of corticosteroids in treating pertussis? Answer: Limited; not routinely recommended due to lack of proven benefit
Question: What is the typical white blood cell count in infants with severe pertussis? Answer: Markedly elevated, often >20,000 cells/μL with lymphocyte predominance
Question: How does pertussis transmission occur? Answer: Through respiratory droplets from coughing or sneezing
Question: What is the recommended isolation period for hospitalized patients with pertussis? Answer: Until 5 days of appropriate antibiotic therapy have been completed
Question: What is the role of cough suppressants in treating pertussis? Answer: Generally not recommended, as they do not affect the course of the disease
Question: What is the most common neurologic complication of pertussis in infants? Answer: Seizures
Question: How does B. parapertussis infection differ from B. pertussis infection? Answer: Generally milder symptoms and shorter duration
Question: What is the estimated global burden of pertussis in children under 5 years old? Answer: Approximately 24.1 million cases and 160,700 deaths per year (as of 2014 WHO estimates)
Question: What is the role of maternal Tdap vaccination in preventing infant pertussis? Answer: It provides passive antibody protection to the infant in the first months of life
Question: What is the recommended timing for maternal Tdap vaccination? Answer: Between 27 and 36 weeks of each pregnancy
Question: What is the significance of pertactin-negative B. pertussis strains? Answer: They may be associated with increased vaccine breakthrough cases
Question: What is the role of serology in diagnosing pertussis? Answer: Useful in later stages of illness when PCR and culture may be negative
Question: What is the recommended duration of antibiotic treatment for pertussis? Answer: 5 days for azithromycin, 7 days for clarithromycin, or 14 days for erythromycin or trimethoprim-sulfamethoxazole