Bordetella Pertussis (Whooping Cough)

In infants (and particularly those ≤3 months) Bordetella pertussis causes a severe upper respiratory tract infection - in older children and adults it is milder, as is infection with Bordetella parapertussis.¹

It is a potentially fatal disease for young children that can be eradicated from the community as effective immunisation is available.

B. pertussis is a small Gram -ve coccobacillus, which causes 300,000 deaths worldwide in children each year.² Pertussis has its highest incidence in infants. School-aged children are often the source of infection for younger siblings at home but infection also occurs in adolescents and adults. Morbidity and mortality are higher in females than males.

In the 1950s, before pertussis immunisation was introduced, the average number of notifications in England and Wales exceeded 100,000 each year.

In 1972, when the uptake of vaccine was over 80%, there were only 2,069 notifications of pertussis. Public anxiety about the safety and efficacy of the vaccine followed a report which suggested the vaccine was associated with a group of children with brain damage, and immunisation coverage dropped to 30% in 1975, resulting in major epidemics in 1977/79 and 1981/83. As a result, there were more than 200,000 extra notifications and 100 deaths in the 1970s and 1980s.

Vaccine coverage steadily increased as public and professional confidence in the vaccine was restored, reaching 94% in 1995, at which level it has remained. Notifications decreased dramatically during this period with 409 notifications and 2 deaths in 2003. Between 1980 and 1983, there were 30 deaths in 4 years. Between 1994 and 2003 there were 27 deaths in 10 years. The Health Protection Agency (HPA) initiated a programme of enhanced surveillance to monitor the number of cases of whooping cough and vaccine efficacy in 1994.³

The level of whooping cough in babies under 6 months old remains high. For this reason it is important that herd immunity be maintained through high vaccination coverage.

Note vaccination history. The patient may be a child who is too young to have started the schedule.

• The first stage is the catarrhal phase with symptoms of mild respiratory infection including sneezing, runny eyes and fever. This progresses after 1 or 2 weeks to the paroxysmal coughing stage.
• As the catarrhal symptoms wane, a dry, hacking cough starts, typically brought on by any sudden startle. Prolonged coughing episodes may be followed by the characteristic 'whoop'. The child chokes, gasps and flails the extremities, with eyes bulging and watering and face reddened. This is called the paroxysmal stage.
• The cough is very persistent, long after infection is past and may last for 2 or 3 months. It was called 'the 100 days' cough'.

• Infants especially are very unwell.
• Illness may be relatively mild in older children and adults.⁴ It may not be brought to medical attention.
• The cough is impressive:
  • If the child does not cough spontaneously, then touching the pharynx with a tongue depressor may trigger a spasm.
  • The child will cough, cough, cough without drawing breath until the lungs are virtually emptied.
  • A small child learns to follow this by breathing in through partially closed vocal cords and this causes the characteristic whoop.
  • Older children and adults do not need to whoop and often do not do so. Infants may be unable to do so and may instead have apnoea and cyanosis after a paroxysm of coughing. Hence the diagnostic feature is not so much the whoop as the persistent cough, cough, cough that empties the lungs before another breath can be drawn.
• The ferocity of the coughing may well cause vomiting. It can also produce subconjunctival haemorrhages. The child is often left exhausted.

Incubation period is usually 7 to 10 days. It is most infectious in the catarrhal phase and can be considered non-infectious to non-household contacts 3 weeks after onset of paroxysms. This is reduced to 5 days if erythromycin or azithromycin is given.

• Adenoviral infection - associated with fever, sore throat and conjunctivitis
• Mycoplasma pneumoniae - usually history of fever, headache and systemic symptoms at onset
• Chlamydophila (Chlamydia) pneumoniae - commonly causes pharyngitis, bronchitis and atypical pneumonia mainly in elderly and debilitated patients

• The bacterium can be difficult to culture and so false negative results may be as high as 20%.
• Traditionally a cough plate was used. An agar plate was held in front of the mouth of a coughing child.
• A nasopharyngeal swab is often used as an alternative. Since 2001 such tests as PCR and serology have been used, especially in adults.

Classical, severe pertussis, as defined by the World Health Organization (WHO), consists of at least 21 days of cough illness with paroxysms, associated whoops or post-tussis vomiting, and culture confirmation. Mild pertussis is any laboratory-confirmed pertussis disease that does not meet the criteria for classical disease.

Generally supportive treatment including nasopharyngeal suction, oxygen and parenteral fluids, is essential for infants under 1 year who are at greatest risk of complications and permanent sequelae. Steroids and beta-2-agonists are also used in the management of severe neonatal pertussis.⁵

• Although this is a bacterial disease, antibiotics do not alter the clinical course once the disease is established. However, erythromycin (7 days),² clarithromycin or azithromycin, given for 7-14 days, may curtail the period of infectivity.²
• If a person has been in contact with the disease then prophylactic antibiotics are of value.⁶ There is most evidence about erythromycin but azithromycin and clarithromycin are better tolerated.
• The severity of the disease is related to the age of the patient, being more severe the younger the person. About 50% of infants are admitted to hospital and morbidity and mortality are greatest below 6 months of age.

Severe complications and deaths occur mostly in infants under six months of age.
Serious illness is less common in older children and adults with an incidence between 1 in 15,000 and 1 in 21,000. However, they have the potential to transmit infection to vulnerable babies:

• Severe complications in infants include pneumonia, encephalopathy and meningoencephalitis⁷
• Infants may experience weight loss, bronchitis, otitis media, apnea, cyanosis, inguinal hernia and rectal prolapse⁷
• Problems in adults include fractured ribs, pneumothorax, inguinal hernia, aspiration pneumonia, seizures, otitis media and urinary incontinence⁸
• They are an under-reported group and a source of infection to the very young⁹

This is not a trivial childhood infection, especially in the very young. The risk is highest in younger babies. Approximately 1 in every 500 babies under 1 with whooping cough dies as a result of the illness. Mortality across all age groups is approximately 0.3%. The cough lasts a long time and future upper respiratory tract infections may produce whooping for a while after.

See Bordetella Pertussis (Whooping Cough) Vaccination.