Whooping cough

Notification should occur when whooping cough (pertussis) is suspected on purely clinical grounds. Whooping cough is an acute, highly contagious respiratory infection, usually caused by Bordetella pertussis. The illness involves at least two weeks of cough, associated with paroxysms, whoops or post-cough vomiting. Cases may be clinically confirmed or laboratory-confirmed.

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

Epidemiology¹²

B. pertussis is a small Gram-negative coccobacillus, which causes 300,000 deaths worldwide in children each year. Whooping cough is a cyclical disease with increases occurring every three to four years; the last peak occurred in 2012.

Whooping cough was endemic in the UK prior to the introduction of the vaccine in the 1950s, with annual notifications exceeding 120,000 in England and Wales. Prevalence plummeted following the widespread uptake of the immunisation programme but epidemics have periodically occurred. In the late 1970s/early 1980s this was due to fall in vaccine coverage due to a public loss of confidence in safety. The latest epidemic in 2012, however, occurred while vaccine uptake was high, and matched increased prevalence elsewhere in the world.

In the UK, whooping cough used to have its highest incidence in infants (school-aged children are often the source of infection for younger siblings) but now infection also occurs in adolescents and adults. In the 2012 outbreak, the highest incidence of disease was in babies under the age of 3 months, who contracted the infection before being old enough to have their first vaccination. As a result of this, the Department of Health introduced a temporary programme of vaccination of pregnant women at 28-32 weeks of gestation. This allows passive protection via the intrauterine transfer of maternal antibodies and, as it appears to have been effective and safe, the programme has become permanent.

3,681 laboratory-confirmed cases were reported in 2019 in England³. 74% of cases were in the >15 age range. Whooping cough is underdiagnosed, with one study in primary care in the UK showing evidence of recent infection in one fifth of school children presenting with persistent cough⁴. The rate was similar in fully vaccinated children, prompting a need to consider a booster dose.

Presentation

Note the vaccination history, including that of the mother for very young babies. Children and adults can catch whooping cough even if they were vaccinated in the past because both natural and vaccine immunity wane over time.

Whooping cough commonly lasts for 6-8 weeks even when treated with antibiotics, with severity of symptoms related to age⁵:

• The first stage is the catarrhal phase with symptoms of mild respiratory infection including malaise, conjunctivitis, nasal discharge, sore throat, dry cough and mild fever. This progresses after one or two 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. There is frequently post-cough vomiting. The paroxysms may be severe enough to bring on cyanosis. This is called the paroxysmal stage.

• The cough is very persistent, long after infection is past and may last for two or three months. It was called 'the 100-day cough'.

Examination

• Infants especially may be very unwell.

• 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.

Infectivity and incubation period

Transmission is by respiratory droplets. The incubation period is 7 to 20 days. It is most infectious in the catarrhal phase and can be considered non-infectious to non-household contacts three weeks after onset of symptoms. This is reduced to five days if the appropriate antibiotics are given.

Children or healthcare workers who are diagnosed with whooping cough should stay off school/work until at least 21 days from the onset of symptoms or after taking antibiotics for at least 48 hours (whichever is the sooner). People who work in other settings should be advised to avoid contact with unvaccinated infants during this time period. This guidance is to help arrest spread of the infection and to protect those most vulnerable to it.

Differential diagnosis

Other causes of upper respiratory tract infection and lower respiratory tract infection:

• Adenoviral infection - associated with fever, sore throat and conjunctivitis.

• Mycoplasma pneumoniae - usually a history of fever, headache and systemic symptoms at onset.

• Chlamydophila pneumoniae - commonly causes pharyngitis, bronchitis and atypical pneumonia, mainly in elderly and debilitated patients.

• B. parapertussis - causes a similar but milder illness. Immunity to B. pertussis does not confer immunity to this different organism.

Other causes of persistent cough:

• Asthma.

• Chronic obstructive pulmonary disease (COPD).

• Post-infectious cough.

• Gastro-oesophageal reflux disease.

• Lung cancer.

Investigations⁶

Whooping cough is a notifiable disease. Therefore, if clinical features raise suspicion, a notification form should be completed within three days and sent to the local Public Health England (PHE) centre. The local centre would then advise on further investigation. This will depend on age, duration of symptoms and local facilities⁵:

• Oral fluid testing. This is recommended in people aged 5-16 who have had cough with features of whooping cough for more than two weeks, and not received a vaccine in the preceding year. It is tested for anti-pertussis toxin immunoglobulin G (IgG). The test kit is sent upon a case being reported to the PHE local centre. This can be sent directly to the person's home or to their GP surgery.

• Serology testing. Blood tests for anti-pertussis toxin IgG are recommended in those over 17 years of age or under 5 years of age who have had the cough for more than two weeks.

• Culture of nasopharyngeal swabs/pernasal swabs/nasopharyngeal aspirates (not throat swabs or anterior nasal swabs). A pernasal swab is inserted through a nostril and advanced along the floor of the nose until it reaches the nasopharynx. Sensitivity is affected by age, duration of illness and vaccination status. A swab is recommended in those with cough of less than two weeks.

• Polymerase chain reaction (PCR) testing is used for severely ill, hospitalised infants. Pernasal swabs are taken in the same way for PCR testing but sent dry, without the transport medium.

Management⁶

Hospital admission is required for any infant aged ≤6 months who is acutely unwell, or at any age if there are respiratory difficulties or significant complications.

Although this is a bacterial disease, antibiotics do not alter the clinical course once the disease is established⁷. However, macrolide antibiotics may curtail the period of infectivity. Antibiotics should therefore be given as soon as possible after the onset of illness in order to eradicate the organism and limit ongoing transmission. Antibiotics should only be started within three weeks of onset of symptoms, given their lack of effect on the course of the illness, and the period of infectivity.

Macrolide antibiotics are first-line:

• Clarithromycin for babies aged less than 1 month.

• Azithromycin or clarithromycin for children aged 1 month or older and for non-pregnant adults.

• Erythromycin for pregnant women.

Co-trimoxazole is advised (off-licence) where macrolides are contra-indicated or not tolerated.

Otherwise, management is supportive and involves symptomatic relief. No symptomatic measures have yet been proven effective in clinical trials⁸.

Offer antibiotic prophylaxis (macrolide antibiotic) to close contacts of the ‘index case’ with suspected or confirmed pertussis, if the 'index case’ occurred within the previous 21 days, and the close contact is in one of the following priority groups:

• Group 1 (infants at increased risk of severe complications from pertussis) includes:
  

  • Unimmunised infants (born before 32 weeks of gestation) less than 2 months of age regardless of maternal vaccine status.

  • Unimmunised infants (born after 32 weeks of gestation) less than 2 months of age whose mothers did not receive maternal pertussis vaccine after 16 weeks and at least 2 weeks before delivery.

  • Infants aged 2 months or over who are unimmunised or partially immunised (fewer than three doses of DTaP/IPV/Hib up to 1 year of age) regardless of maternal vaccine status.

• Group 2 (people at increased risk of transmitting infection to infants in Group 1 and who have not received a pertussis-containing vaccine more than 1 week and less than 5 years ago) includes:
  

  • Pregnant women at 32 weeks of gestation or more.

  • Healthcare workers who work with infants and pregnant women.

  • People whose work involves regular close or prolonged contact with infants too young to be fully vaccinated.

  • People who share a household with an infant too young to be fully vaccinated.

Complications

The more severe complications and deaths occur mostly in infants aged less than 6 months. Complications include:

• Pneumonia.

• Apnoea.

• Seizures.

• Encephalitis.

• Otitis media.

• Dehydration.

• Weight loss.

• Problems caused by raised intra-thoracic or intra-abdominal pressure during coughing such as:

  • Fractured ribs.

  • Subconjunctival haemorrhage.

  • Inguinal hernia or other hernias.

  • Rectal prolapse.

  • Pneumothorax.

  • Urinary incontinence.

  • Petechiae.

Prognosis

The most severe infections are usually in infants, with morbidity and mortality greatest in those aged less than 6 months. Mortality rate at this age is much higher than that of the general population (an estimated 3.5% as compared to 0.03%)⁵. Serious illness is less common in older children and adults.

The cough can last for three months or more and future upper respiratory tract infections may produce whooping for a while afterwards.

Prevention¹

See the separate Whooping Cough Vaccination article. As above, the vaccination programme in the UK has been extended to include pregnant women to give neonates protection before the time of their first routine vaccination.

Current recommendations to treat cases with antibiotics are in the interests of reducing spread to others rather than influencing the course of the disease for the individual. Exclusions from school or the workplace should follow guidance set out in the 'Infectivity and incubation period' section above.

Close contacts should be offered prophylaxis - as above.