Pertussis

• A highly contagious acute bacterial infection caused by the bacilli Bordetella pertussis.
• Currently, worldwide prevalence is diminished due to active immunization.
• However, it remains a public health problem among older children & adults.
• It continues to be an important respiratory disease afflicting unvaccinated infants and previously vaccinated children and adults (waning immunity).

Transmission

• Through the respiratory route (droplet infection).
• Adolescents and adults are the reservoir. No animal or insect reservoir.
• A highly communicable disease. 80% among household contacts.
• In the catarrhal stage and 2 weeks after the onset of cough.

Etiology

• Bordetella pertussis – aerobic gram-negative coccobacilli.
• Produces toxins namely pertussis toxin, filamentous hemagglutinin, hemolysin, adenylate cyclase toxin, dermonecrotic toxin, and tracheal cytotoxin - responsible for clinical features (toxin-mediated disease) and the immunity.

Pathogenesis

The organism gets attached to the respiratory cilia and toxin causes paralysis of cilia. ⇒ Muocopurulent-sanguineous exudate forms in the respiratory tract. This exudate predisposes to atelectasis, cough, cyanosis, and pneumonia. ⇒ The organism causes local tissue damage and systemic effects mediated through its toxin.

Clinical Manifestations

• Incubation period: 7-10 days.

  • Infection lasts for 6 weeks – 10 weeks.

• Stage I (catarrhal stage; 1-2 weeks): insidious onset of coryza, sneezing, low-grade fever, and occasional cough.

• Stage II (paroxysmal cough stage; 1-6 weeks): due to difficulty in expelling the thick mucous from the tracheobronchial tree.

  • At the end of paroxysm, long inspiratory effort is followed by a whoop.
  • In between episodes, the child looks well. During episodes of cough, the child may become cyanosed, followed by vomiting, exhaustion, and seizures.
  • Cough increases for the next 2-3 weeks and decreases over the next 10 weeks.
  • Absence of whoop and/or post-tussive vomiting does not rule out clinical diagnosis of pertussis.
  • Paroxysmal cough >2 weeks with or without whoop and/or post-tussive vomiting is the hallmark feature of pertussis.

• Stage III (convalescence stage): period of gradual recovery even up to 6 months.

Complications

1. Secondary pneumonia (1 in 5) and apneic spells (50%; neonates and infants <6 months of age).
2. Neurological complications: seizures (1 in 100) and encephalopathy (1 in 300) due to the toxin or hypoxia or cerebral hemorrhage.
3. Otitis media, anorexia and dehydration, rib fracture, pneumothorax, subdural hematoma, hernia, and rectal prolapse.

Differential Diagnosis

1. B. parapertussis, adenovirus, mycoplasma pneumonia, and chlamydia trachomatis.
2. Foreign body aspiration, endobronchial tuberculosis, and a mass pressing on the airway.

Diagnosis

1. Suspected on the basis of history and clinical examination and is confirmed by culture, genomics, or serology.
2. Elevated WBC count with lymphocytosis. The absolute lymphocyte count of ≥20,000 is highly suggestive.
3. Culture: gold standard especially in the catarrhal stage. A saline nasal swab or swab from the posterior pharynx is preferred and the swab should be taken using dacron or calcium alginate and has to be plated onto the selective medium. However, cultures are not recommended in clinical practice as the yield is poor because of previous vaccination, antibiotic use, diluted specimen, and faulty collection and transportation of specimen.
4. PCR: most sensitive to diagnose; can be done even after antibiotic exposure. It should always be used in addition to cultures.
5. Direct fluorescent antibody testing: low sensitivity & variable specificity.

Treatment

1. Avoidance of irritants, smoke, noise, and other cough-promoting factors.
2. Antibiotics: effective only if started early in the course of illness. Erythromycin (40-50 mg/kg/day 6 hr orally for 2 weeks or Azithromycin 10 mg/kg for 5 days in children <6 months and for children >6 months 10 mg/kg on day 1, followed by 5mg/kg from day 2-5 or Clarithromycin 15 mg/kg 12 hrly for 7 days.
3. Supplemental oxygen, hydration, cough mixtures, and bronchodilators (in individual cases).

Prevention

• All household contacts should be given erythromycin for 2 weeks.
• Children <7 years of age not completed the four primary doses should complete the same at the earliest.
• Children <7 years of age completed primary vaccination but not received the booster in the last 3 years have to be given a single booster dose.
• Vaccine