Pertussis (Whooping Cough)

Pertussis, or whooping cough, is a respiratory infection caused by the bacterium Bordetella pertussis, characterised by prolonged paroxysmal coughing that can be severe in young infants. Despite long-standing vaccination, it has resurged in several settings, making it a salient vaccine-preventable disease (Cherry, 2012).

Definition

Pertussis is a respiratory infection by Bordetella pertussis producing a prolonged cough illness, often with paroxysms and an inspiratory whoop, transmitted by respiratory droplets and preventable by vaccination, though immunity from vaccine or infection wanes over time.

Scope

This topic covers pertussis as a clinical and public-health entity: its bacterial cause, the toxin-mediated illness and its protracted course, the difference between disease and infection, and the epidemiology of resurgence under vaccination. It is a reference overview and does not provide treatment or prescribing guidance.

Core questions

• What causes the prolonged, paroxysmal cough of pertussis?
• Why is pertussis especially dangerous in young infants?
• How does the epidemiology of pertussis disease differ from that of B. pertussis infection?
• Why has pertussis resurged despite widespread vaccination?

Key concepts

• Bordetella pertussis
• Pertussis toxin and other virulence factors
• Catarrhal, paroxysmal, and convalescent stages
• Inspiratory whoop
• Waning immunity
• Disease versus infection
• Resurgence under vaccination

Mechanisms

Bordetella pertussis colonises the respiratory epithelium and produces pertussis toxin and other virulence factors that contribute to the characteristic illness. The disease classically evolves through a catarrhal stage resembling a common cold, a paroxysmal stage with bouts of severe coughing and the inspiratory whoop, and a prolonged convalescent stage. Immunity following vaccination or natural infection wanes over time, so older children and adults can again become susceptible and act as a reservoir, while a meaningful share of B. pertussis infection is mild or asymptomatic and so differs from recognised disease (Cherry, 2005; Cherry, 2012).

Clinical relevance

Pertussis shows how waning immunity and the gap between infection and recognised disease can sustain transmission even in well-vaccinated populations, and why infants are a particular focus of concern. This entry is descriptive and educational; it characterises the disease and its epidemiology and is not a basis for diagnosis or treatment in an individual patient.

Epidemiology

Pertussis remains endemic worldwide and has resurged in several settings despite high vaccination coverage, a pattern attributed substantially to waning immunity and to differences between circulating disease and infection (Cherry, 2012; Cherry, 2005). The youngest infants, who are incompletely immunised, bear the greatest burden of severe disease.

History

Whooping cough has been described as a distinct epidemic illness since at least the sixteenth century, and Bordetella pertussis was identified as its cause in the early twentieth century. Whole-cell and later acellular vaccines greatly reduced its incidence, but the recognition of waning immunity and of resurgence in vaccinated populations reframed pertussis as a continuing challenge (Cherry, 2012).

Debates

Why has pertussis resurged in well-vaccinated populations?

Proposed contributors include waning immunity after acellular vaccines, improved diagnosis and surveillance, and pathogen adaptation; their relative weight, and the implications for vaccination strategy, remain debated.

Key figures

• James D. Cherry

Seminal works

• cherry-2012
• cherry-2005

Frequently asked questions

Why is whooping cough particularly serious in babies?

Young infants are at highest risk of severe pertussis, including complications, before they have completed their primary vaccinations. Much of the strategy around pertussis focuses on protecting this group.

Why does pertussis still occur where vaccination is common?

Immunity from pertussis vaccination and from natural infection wanes over time, so older children and adults can become susceptible again and transmit the bacterium. This waning immunity is a leading explanation for resurgence in well-vaccinated populations.