Cause

The bacterium Bordetella pertussis (B. pertussis).

Transmission

B. pertussis is transmitted mainly by airborne droplets from the respiratory mucous membranes of infected individuals.

Nature of the disease

Pertussis (whooping cough) is a highly contagious acute bacterial disease involving the respiratory tract. Typical manifestations include several weeks of cough which gradually develop into severe coughing fits, ending in a characteristic “whoop”, often with cyanosis and vomiting. In young infants, the cough may be absent and the disease may manifest with spells of apnoea. Although pertussis can occur at any age, most serious cases and fatalities are observed in early infancy. Major complications include pneumonia, encephalitis and malnutrition (due to repeated vomiting).

Geographical distribution

WHO estimated that in 2008, about 16 million cases of pertussis occurred worldwide, 95% of which were in developing countries, and that some 195 000 patients died from this disease.

Risk for travellers

Unprotected young infants are at highest risk of severe pertussis, but older children, adolescents and adults may also contract the disease (often in mild and atypical form) if they are not fully immunized. Exposure to pertussis is more frequent in developing countries. All infants, including those who are HIV-positive, should be immunized against pertussis.