Pertussis (Whooping Cough)

Epidemiology of Infectious Diseases: Pertussis (Whooping Cough)

Causal agent
An acute bacterial respiratory infection caused by Bordetella pertussis.

Common clinical features

  • Characterized by 3 stages;
  • The catarrhal stage - onset of coryza, sneezing, low-grade fever, and a mild cough (1-2 weeks), followed by the paroxysmal stage - bouts of coughing ending with a high-pitched inspiratory whoop or vomiting (lasting 1-6 weeks but may persist for up to 10 weeks).
  • During the convalescence stage recovery is gradual and the cough becomes less paroxysmal and disappears in 2-3 weeks (recovery may take weeks to months).
  • The most severe infections are in infants of which over 50% are hospitalized (HPA).
  • In adults symptoms range from mild respiratory infection to paroxysmal cough episodes.
  • Complications include, pneumonia, seizure, encephalopathy, weight loss and death.
  • Complications are most likely to occur in young infants among who the most common cause of pertussis related deaths is secondary bacterial pneumonia.
  • Pertussis can occur in previously immunized and infected individuals, but immunization and prior infection attenuate the clinical picture.  

Epidemiology

  • Endemic worldwide.
  • Pertussis is a major cause of childhood morbidity and mortality in developing countries, where an estimated 50 million cases and 300,000 deaths occur each year.
  • In the UK notifications have declined significantly since the introduction of pertussis immunization with 594 cases reported in 2005.  

Reservoir
Humans

Mode of transmission
Droplet spread from an infectious case.

Incubation period
Average 9-10 days with a range of 6-20 days.

Period of Communicability
Persons with pertussis are highly infectious during the catarrhal stage and during the first 2 weeks of the paroxysmal stage. A case is normally not infectious 3 weeks after the onset of the paroxysmal stage, though in up to 20% of cases infectivity may persist for up to 6 weeks2. 

When treated with erythromycin patients are no longer contagious after 5 days of treatment1.

Prevention and control

  • Maintain high immunization coverage
  • In the UK accellular pertussis vaccine is given in the primary course with diphtheria, tetanus, polio and Hib (as DtaP/IPV/Hib), given at aged 2,3, & 4 months of age. A further booster dose is given with the preschool boosters between the ages of 3 and 5 (Health Protection Agency).
  • Respiratory isolation for cases until at least 5 days (or until 14 day course of erythromycin completed).
  • Arrange for laboratory confirmation2.
  • Vaccination of unvaccinated household contacts and exclusion from school etc.
  • Antibiotic prophylaxis may be of value for unvaccinated household contacts of cases, particularly in infants <6 months of age, if given within 21 days of onset of the first case2.

References

  1. Heymann D L, editor, Control of Communicable Disease Manual. 18th ed. American Public Health Association; 2004.
     
  2. Hawker J, Begg N, Blair I, Reintjes R, Weinberg J. Communicable Disease Control Handbook, Blackwell, 2005.

© CM Kirwan 2006