Pertussis is a highly infectious and contagious disease caused by Bordetella pertussis and is commonly referred to as whooping cough.

Epidemiology

• Incidence - 1-5/100,000
• Transmission
  • Adult and teenage children with common cold symptoms are significant reservoirs of the organism and source of outbreaks in highly susceptible populations (transmission rates >90% in susceptible populations)
    • Primarily seen in those with waning immunity to childhood vaccination
    • Immunity begins to wane during early adolescence
    • Secondarily seen in unimmunized infants
  • B. pertussis, transmitted by respiratory droplets, causes disease only in humans
  • Infection occurs most frequently in late spring and summer

Organism

• Bordetella pertussis, a gram-negative pleomorphic coccobacillus
• Produces multiple toxins that aid in organism attachment and production of disease
• B. parapertussis is a related species that may cause a milder form of pertussis syndrome

Clinical Presentation

• Nonspecific viral upper respiratory tract infection symptoms
  • Disease spread often not recognized due to mild symptoms in immunized persons
  • Secondary spread common in families and schools
• After 7-10 day incubation, a prolonged course ensues which consists of 3 overlapping stages
  • Catarrhal (1-2 weeks)
  • Paroxysmal coughing (1-4 weeks)
  • Convalescent (4-6 weeks)
• Partially immune persons and infants older than 6 months may not manifest all of the typical symptoms
  • Paroxysmal coughing may be absent
• Classical pertussis generally diagnosed clinically
  • Paroxysmal cough
  • Inspiratory whoop
  • Posttussive vomiting
  • Lymphocytosis
• Atypical pertussis may occur with mild or absent symptoms in adults or previously vaccinated children
  • Atypical pertussis is common, endemic and usually unrecognized in adults
•  Secondary complications
  • Respiratory 
    • Pneumonia
    • Bronchitis
    • Laryngitis
    • Pneumothorax
  • Nonrespiratory
    • Complications as a result of severe cough
      • Rib fracture
      • Epistaxis
      • Subconjunctival hemorrhage
    • Central nervous system
      • Seizures
      • Encephalitis
      • Deafness
    • Hemolytic Uremic syndrome

Treatment

• Antibiotics
  • If treatment given after 3-4 days of symptoms only contagiousness is reduced
  • Prophylaxis for household contacts

Prevention

• Vaccination
• Pediatric age groups - combined Hib and DPT
• Adult revaccination
  • During teen years and in patient 30 years and older (diphtheria, pertussis acellular and tetanus vaccine)

Diagnosis

• Indications for testing
  •  Patients with predominant complaint of cough, especially in the absence of fever, sore throat, hoarseness, tachypnea of wheeze
• Laboratory testing
  • PCR
    • Highly sensitive and specific for pertussis - must use nasopharyngeal swab for highest sensitivity and specificity
    • Treatment reduces contagious phase in 5 days and may negate PCR results
  • Nasopharyngeal culture
    • Considered gold standard, but is frequently negative in adults
    • Recommended only during the first 3 weeks of illness
  • Serological testing 
    • Requires sequential specimens negating clinical utility of early serological diagnosis
    • Useful for epidemiology or when diagnosis is considered late in the course of the disease
    • Useful for evaluating response to pertussis vaccine

Refer to Bordetella pertussis topic at www.arupconsult.com for a chart of Comparison of Definitions for Pertussis Infection

Differential Diagnosis

• Chlamydia pneumoniae
• Adenovirus
• Mycoplasma
• Parainfluenza
• Influenza
• Asthma
• Chronic bronchitis
• Cytomegalovirus (CMV)