Causes

• Respiratory syncytial virus (RSV)^[3]
• Human metapneumovirus (hMPV) - causes similar spectrum of illness to RSV and is thought to be the second most common cause
• Adenovirus - occasionally causes a similar syndrome with a more virulent course
• Parainfluenza virus
• Other less common causes include:
  • Mycoplasma pneumoniae
  • Enterovirus
  • Influenza virus
  • Rhinovirus
  • Chlamydophila pneumoniae

Epidemiology

• Peak incidence of respiratory syncytial virus (RSV) infections is in the winter months (November to March), although the size of the peak varies from winter to winter.^[3]
• Prevalence may be higher in urban areas.
• By their first birthday over 60% of children have been infected and, by two years of age, over 80%. The antibodies that develop following early childhood infection do not prevent further RSV infections throughout life.^[3]
• 3% of infants are admitted to hospital with bronchiolitis. Rates of hospitalisation for bronchiolitis have been rising: the cause is thought to be multifactorial, but includes improved survival of premature infants.

Risk factors^[2]

Environmental and social risk factors:

• Older siblings
• Nursery attendance
• Passive smoke, particularly maternal
• Overcrowding

Breast-feeding is considered protective and should be encouraged for this and other reasons.

Risk factors for severe disease and/or complications:

• Prematurity (<37 weeks)
• Low birthweight
• Age less than 12 weeks
• Chronic lung disease (eg cystic fibrosis, bronchopulmonary dysplasia)
• Congenital heart disease with left to right shunt
• Neurological disease with hypotonia and pharyngeal dis-coordination
• Immunocompromise
• Congenital defects of the airways
• Down's syndrome^[4]

Presentation

Symptoms

• Early symptoms are those of a viral upper respiratory tract infection (URTI), including mild rhinorrhoea, cough, and fever. Fever >39°C is unusual and should prompt a thorough examination and further investigations to exclude other possible causes.
• Adults, older children and many infants do not progress to any further symptoms.
• For the 40% of infants and young children who progress to lower respiratory tract involvement, paroxysmal cough and dyspnoea develop within 1-2 days.
• Other common symptoms include the following: wheeze, cyanosis, vomiting, irritability and poor feeding.
• Apnoeas may occur, especially in young infants.

Signs

Follow the National Institute for Health and Clinical Excellence (NICE) guidance for the assessment of feverish illness in children (in those under 5):^[5]

• Look for tachypnoea, tachycardia, fever, cyanosis and signs of dehydration. It is unusual for a child to appear 'toxic' (suggested by drowsiness, lethargy, pallor, mottled skin) and this should prompt urgent action in terms of the need for immediate treatment and exclusion of other potential causes.
• Mild conjunctivitis, pharyngitis.
• Evidence of increased respiratory work: intercostal, subcostal and supraclavicular recession, nasal flaring.
• Widespread fine inspiratory crackles are considered a key finding in the UK, whilst high-pitched expiratory wheezing is commonly present but not essential to a diagnosis. American definitions put more emphasis on the presence of wheeze.
• Liver and spleen may be palpable due to hyperinflation of the lungs.

Differential diagnosis

• Asthma and other causes of wheezing in childhood
• Bronchitis
• Pulmonary oedema
• Foreign body inhalation
• Pneumonia
• Oesophageal reflux
• Aspiration
• Cystic fibrosis
• Kartagener's syndrome
• Tracheomalacia/bronchomalacia
• Pneumothorax

Investigations

• Pulse oximetry
• Nasopharyngeal aspirate for:
  • Respiratory syncytial virus (RSV) rapid testing - to enable isolation or cohort arrangements and to prevent further, unnecessary testing.
  • Viral cultures for RSV, influenza A and B, parainfluenza and adenovirus can also be undertaken.

Other investigations that are not recommended for typical acute bronchiolitis include:^[1]

• Chest X-ray: bronchiolitis produces:
  • Nonspecific hyperinflation and patchy infiltrates
  • Focal atelectasis
  • Air trapping
  • Flattened diaphragm
  • Increased anteroposterior diameter
  • Peribronchial cuffing
  Chest X-ray should only be performed if there is diagnostic uncertainty or an atypical course.
• Full blood count
• Electrolytes and renal function: - only perform if the child is dehydrated or on IV fluids.
• Blood and urine culture: consider if pyrexia >38.5°C or the child has a 'toxic' appearance.
• Arterial blood gases: may be required in the severely ill patients, especially in those who may need mechanical ventilation.

Management

Primary care

• Most infants with acute bronchiolitis will have mild, self-limiting illness and can be managed at home. Supportive measures are the mainstay of treatment, with attention to fluid input, nutrition and temperature control.
• Within General Practice, a doctor's role is to assess current severity of illness and, for those with mild-to-moderate disease, to support and monitor. Consider whether the presentation is in the early stages of disease, when a child is more likely to get worse before improving. Careful safety netting is important, teaching parents to spot deterioration and to seek medical review should this occur.
• For the majority, bronchiolitis lasts 7-10 days, with 50% asymptomatic by 2 weeks and only a small subgroup still symptomatic at 4 weeks.

Referral

Hospital referral is suggested where there is:^[1]

• Poor feeding (<50% usual intake over previous 24 hours) which is inadequate to maintain hydration
• Lethargy
• History of apnoea
• Respiratory rate >70 breaths/minute
• Nasal flaring or grunting
• Severe chest wall recession
• Cyanosis
• Saturations ≤94%
• Uncertainty regarding diagnosis
• Where home care or rapid review cannot be assured

The threshold for admission should be lower in those with significant comorbidities, premature infants and those under 3 months old.

Paediatric intensive care unit (PICU) admission is necessary if the child has increasing severe respiratory distress with desaturation or apnoea whilst receiving 50% O₂. Continuous positive airway pressure (CPAP) or intubation may be required in these cases.

Secondary care

• Even amongst hospitalised children, supportive care is the mainstay of treatment, including oxygen and nasogastric feeding where necessary.
• Other treatments have shown inconsistent or little evidence of benefit:
  • Bronchodilators - modest short-term improvement in clinical scores but no reduction in the rate or duration of hospitalisation.^[6]
  • Corticosteroids - trials have consistently failed to provide evidence of benefit.^[7] A large multicentre randomised controlled trial (RCT) comparing the use of a single dose of oral dexamethasone with placebo in children diagnosed with bronchiolitis in Emergency Departments failed to show any significant differences in the rates of hospital admission, respiratory status after 4 hours or longer-term outcomes.^[8]
  • Adrenaline - some evidence that it may be more effective than salbutamol or placebo in an outpatient setting; no evidence of benefit when used in inpatients.^[9]
  • Hypertonic (3%) saline - thought to act by unblocking mucus plugs and reducing airways obstruction. A Cochrane Review concluded that there was evidence its use did reduce length of hospital stay and clinical severity scores.^[10]
  • Antibiotics - no evidence to support their routine use. Avoid unless there is a strong suspicion or confirmation of a coexisting bacterial infection
  • Ribavirin - may reduce the need for mechanical ventilatory support and the number of days in hospital but no clear evidence of clinically relevant benefits (eg preventing respiratory deterioration or mortality).^[11]
• Chest physiotherapy does not reduce the length of hospital stay and its role in management is still being evaluated.^[12]

Prognosis

• Most children with bronchiolitis make a full recovery.
• Mechanical ventilation is required for 3-7% of admitted patients.^[13]
• In the UK, the respiratory syncytial virus (RSV) related mortality rate in those aged under a year is 84/100,000 population.^[1]
• Most deaths occur in infants younger than 6 months or in those with underlying cardiac or pulmonary disease.
• There is an association between bronchiolitis and subsequent reactive airways disease - approximately 34-50% wheeze following bronchiolitis.^[2] The underlying mechanism by which RSV or other agents, such as rhinovirus, cause reactive airways disease is unknown.

Prevention

Vaccine

There is currently no vaccine available to prevent respiratory syncytial virus (RSV) infection. In the 1960s, an inactivated RSV vaccine was found to enhance RSV disease in subsequent natural infections.

Immunoprophylaxis

Recent years have seen the development of agents which provide passive immunity to RSV: RSV immunoglobulin (RSV-Ig) which has largely been superseded by palivizumab, a monoclonal antibody. It has been shown to reduce RSV-related hospitalisation and intensive care admissions significantly. The Joint Committee on Vaccination and Immunisation recommends that it should be used by those at high risk of severe RSV disease:^[14]

• Children under 2 years with chronic lung disease, who have required at least 28 days' supplemental oxygen from birth or who are receiving home oxygen.
• Infants less than 6 months old with a left-to-right shunt, haemodynamically significant congenital heart disease or pulmonary hypertension.
• Children under 2 years with severe congenital immunodeficiency.

The first dose should be administered before the start of the RSV season.

Infection control

Disease transmission should be limited by:^[1]

• Handwashing
• Use of gloves, aprons or gowns when in direct contact with the patient
• Isolate infected patients or nurse in cohorts based on laboratory confirmation of RSV status