Introduction

Whooping Cough (aka Pertussisis a highly contagious infectious disease, which causes a type of bronchiolitis, caused by the bacterium Bordetella Pertussis. It is highly infectious, and can be deadly, especially in children under 3 months. It causes roughly around 300 000 deaths worldwide each year, although in the developed world deaths are rare. Other LRTI’s are more deadly in these countries.
  • Cases in older children and adults tends to be mild.
  • A similar, but milder infection is caused by the bacterium bordetella parapertussis
Clinically, the main feature is a cough, typically paroxysmal, which lasts > 2 weeks, most commonly around 6-8 weeks. Diagnosis may be clinical, but in recent years is frequently confirm by respiratory virus PCR testing from a swab, or serologically in a blood test.
Treatment is typically with a macrolide (e.g. calrithromycin, erythromycin) or doxycycline. The treatment reduces the period of infectivity but has little effect on the duration of the cough.
  • After 3 weeks of symptoms patients can be considered no longer infectious
  • As such, it is generally considered not worthwhile to commence treatment after this time
  • Patient are considered non-infectious after 48 hours of antibiotics, or 21 days of symptoms, whichever is sooner
A vaccine for bordetella pertussis is part of the vaccination schedule in both the UK and Australia. The illness is commonly still contracted despite a history of vaccination, although tends to be milder in these cases.

Epidemiology and Aetiology

  • Endemic in the worldwide population
  • Epidemics every 3-4 years
  • Relatively low incidence in the UK, due to vaccination program
  • Peak age of incidence – 3 years
  • Only 1% of cases in the UK require hospitalisation
  • Generally, more severe in the very young (<3 months old)
    • The first vaccination for whooping cough is given at the age of 6 weeks in Australia and 8 weeks in the UK
    • Pregnant women are vaccinated usually in the third trimester – to provide some mother-to-baby immunity in the first weeks of life

Clinical features

The infection generally lasts about 6-8 weeks:
Catarrhal phase – 1-2 weeks –  symptoms of coryza. Most contagious during this phase.
Paroxysmal phase – 3-6 weeks – there is a characteristic cough.
  • Present day and night, but often worse during the night
  • Spasmodic – usually child will spasm of cough, classically followed by an inspiratory whoop as the child tries to catch their breath at the end of the spasm. It is this inspiratory whoop after which the condition is named. In children it is ‘high-pitched’ but in adults, usually not. It is not commonly seen in modern times of vaccination – where the disease is often less severe in the case of prior vaccination.
    • Cough is unrelenting until the lungs are emptied. The Whoop signifies the overwhelming reflux to draw in air
    • Children are often exhausted
    • Coughing may cause subconjunctival haemorrhage
    • Older children and adults don’t usually have the whoop
  • Spasm may induce vomiting
  • During the cough spasms, the child may go red or blue in the face. Mucus may be expelled from the nose and mouth
  • Epistaxis (nose bleed) and subconjunctival haemorrhage may occur during spasms.
  • There is usually no fever or wheeze
Convalescent phase – days to months
  • Symptoms gradually decrease, but may still be present after several months in some cases
  • Previously known as the 100 day cough

Differentials

Mainly include other causes of URTI, and URTI with a prolonged cough. Causes include:

  • Adenovirus
  • Atypical pneumonia causing agents
    • Mycoplasma pneumonia
      • Typically has more systemic symptoms – e.g. myalgias
    • Chlamydophilia pneumoniae
      • Mainly older and debilitated patients
      • Pharyngitis, bronchitis and atypical pneumonia
  • Bordatella parapertussis
  • Protracted bacterial bronchitis
    • A diagnosis made in children with >1 month of cough, treatment usually with oral amoxicillin
    • Cough not paroxysmal
    • URTI symptoms generally mild
    • Child generally well
  • Asthma
  • Post-infectious cough
  • GORD

Complications

Generally rare but can be life-threatening. These can include pneumonia, convulsions and bronchiectasis.
Younger children may not have a cough, but mat instead suffer from apnoea.
Although adults can still quite easily contract the disease, it is less dangerous in adults.

Investigations

In the UK, investigation should be guided by the local public health authority (PHE). Whooping cough is a notifiable disease. The advised protocol is to notify the PHE and they will advise testing.

In Australia, it is also a notifiable disease. Testing is performed by practitioner (usually the GP), and notification made when the diagnosis is confirmed.

  • Nasal-pharngeal swab – “Pertussis PCR” – to identify the organism. Usually only effective within the first 3 weeks of the infection, and even then, an unreliable test.
    • Many labs also report respiratory virus PCR results alongside this (including influenza) to assist with a differential
    • Collecting the swab itself involves inserting the swab into the nostril, and all the way along the base of the nasal cavity, until it hits the back of the pharynx. Not a pleasant experience for the patient!
    • Usually negative after 21 days of onset of symptoms, or after 5 days of antibiotics
  • FBC – there is often a lymphocytosis (>15 x109/L)
  • Antibody test – serology test for antibodies against pertussis toxin or Bordetella pertussis related products
    • Not usually useful as a diagnostic test
    • Can confirm a diagnosis retrospectively
    • Antibodies take up to 3-4 weeks to develop – by which time, patients are usually no longer infectious and there usually is no benefit to starting treatment
    • Test stays positive for up to two years
    • Only confirms a diagnosis retrospectively

Complications

  • Pneumonia
  • Apnoea
  • Seizures
  • Encephalitis

Management

  • Consider admitting young children, particularly those <6 months and especially <3 months, to hospital if they are having trough coughing spasm (paroxysms) – as they are likely to become exhausted and deteriorate
    • These presentations are rare
  • Erythromycin is the treatment of choice. If treatment begins in the catarrhal phase then symptoms will resolve relatively quickly, and infectivity is also reduced. However, this is rare, as during this phase diagnosis of whooping cough is extremely unlikely as differentiating it from other causes of URTI is difficult. If treatment starts in the paroxysmal phase, then although the causatory organism is still eradicated, symptoms will usually persist for several weeks.
    • Age <6 months – 10mg/Kg/day for 5 days. PO.
    • Age >6 months – 10mg/Kg/day (max 500mg) on day one, then 5mg/Kg/day (max 250mg) daily for 4 days
    • Alternatives include clarithromycin (7.5mg/Kg – max 500mg, BD for 7 days) and Trimethoprim + sulfamethoxazole (co-trimoxazole)
      • Co-trimoxazole where macrloides are not tolerated
      • Clarithromycin usually used for children unable to swallow tablets as it is available in liquid form. Also it is first line for children aged <1 month.
    • Prophylactic antibiotics are offered to:
      • All household contacts
      • Vulnerable contact (e.g. children <6 months old)
  • Isolation (e.g school and work exclusion) until 21 days since the onset of the cough or 5 days of antibiotics (whichever is less)
  • Contact the Public Health Authority
    • Especially for cases involving school, child care, health workers or other high risk contacts
    • Notifiable disease

Vaccination

This does not provide immunity! However, it reduces the risk of contracting the condition, as well as the severity of the infection if you are unlucky enough to get it. The level of protection declines as childhood progresses.
Why is the rate of infection so low, if protection reduces with age? – Herd Immunity! – young children are the most likely to pass on respiratory infections. As they are immunised, then the disease finds it difficult to establish itself in the population.
Vaccination Schedulepertussis requires 4 vaccinations:
  • Age 2 months
  • Age 3 months
  • Age 4 months
  • Age 3 years and 4 months

References

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