Pertussis

Pertussis (whooping cough) is a highly contagious disease of the respiratory tract caused by Bordetella pertussis bacteria.

Pertussis is transmitted from infected to susceptible individuals by droplets through coughing or sneezing or when in close proximity i.e. sharing breathing space. The B. pertussis bacteria in the droplets attach to the cilia that line part of the upper respiratory system. Subsequently they release toxins, which damage the cilia and cause airways to swell.
The incubation period is approximately 7 to 10 days, with an insidious onset and initial symptoms indistinguishable from a minor upper respiratory infection (the catarrhal stage). Fever is usually minimal throughout the course of infection. The cough, initially intermittent, progresses within 1 or 2 weeks to become paroxysmal. The paroxysms increase in both frequency and severity, and then gradually subside over a period of 2 to 6 weeks, but sometimes much longer (so-called hundred day cough) [1-3]. During the paroxysmal stage, a series of rapid coughs without intervening inspiration will often be followed by the characteristic whoop. During a paroxysm, cyanosis may occur and vomiting may follow [1]. In young infants, the paroxysms may also be followed by periods of apnea. Pneumonia is a relatively common complication; seizures and encephalopathy occur more rarely. Untreated patients may be contagious for three weeks or more following onset of the cough [3].

Pertussis can affect all age groups, however it is most dangerous for infants, who account for nearly all pertussis hospitalizations and deaths. Pertussis in older children, adolescents and adults is most often unrecognized because its clinical course is often atypical [2].  Newborns who get pertussis are often infected by older siblings, parents, or caregivers who might not even know they have the disease.

Treatment: administration of antibiotics early in the course of illness will reduce the duration and severity of symptoms, lessen the infectivity, and reduce the risk of death. Administration of antibiotics during the paroxysmal stage does not change the clinical course, but may eliminate the bacterium form the nasopharynx and thus reduce transmission [2].

Following the introduction of first generation Pertussis vaccines in the 1940s, there has been a dramatic decrease in disease. Today, two forms of vaccine are in use, the whole-cell pertussis vaccines (wP), and the acellular vaccines (aP). Whole-cell pertussis vaccines were developed first and are suspensions of the entire B. pertussis organism that has been inactivated. Immunization with wP vaccines is effective, but immunization has been frequently associated with minor adverse reactions increasing with age; wP vaccines are therefore not recommended for immunization of adolescents and adults. To address the adverse reactions observed with the whole-cell vaccines, aP vaccines were developed in the 199Os and  contain only a small number of highly purified components of B. pertussis such as inactivated pertussis toxin either alone or in combination with other B. pertussis components. aP vaccines combined with diphtheria and tetanus components and sometimes also with IPV (inactivated polio vaccine) are recommended in many countries for booster immunization of adolescents and adults including pregnant women [3]. Despite national immunisation programs, Pertussis still remains endemic in many countries and in 2019, there were more than 133,000 cases of pertussis globally [4].

For more details, please see WHO disease description for Pertussis.