It mainly affects infants below the age of one year, with the majority of cases in babies younger than six months. Up to 2 per cent of all infants will need admission to hospital with bronchiolitis.
The most common virus implicated is respiratory syncytial virus (RSV). However parainfluenza, influenza and adenoviruses can occasionally be responsible. Prematurity and underlying congenital abnormality increase morbidity and mortality.
Bronchiolitis is characterised by inflammation of the bronchioles, necrosis of the ciliated bronchial epithelium and oedema causing airway obstruction. There is associated hyperinflation and patchy segmental collapse of the lungs.
Bronchiolitis presents with fever and coryzal symptoms followed by cough and increasing respiratory difficulty, showing as tachypnoea. This is associated with chest hyperinflation, widespread fine crepitations and often, but not always, audible wheeze and scattered rhonchi on auscultation. Poor feeding, excessive sleepiness, irritability, diarrhoea, vomiting, conjunctivitis, pharyngitis and otitis media may be observed.
Infants younger than six weeks may present with life-threatening apnoea of central origin rather than of an obstructive type. Central apnoea and cyanosis is seen in 10–20 per cent of babies admitted with bronchiolitis.
The symptoms and signs gradually worsen from the second to the seventh days after the start of coryzal symptoms. It is important to keep an open mind about diagnosis, as other conditions can present in a similar manner.
It is essential to take a proper history and examine carefully. If the illness is prolonged, atypical or severe, other underlying risk factors (see box, above) should be considered.
Viral infection-associated wheeze usually affects babies between six and 12 months old, typically those who are overweight and with no strong family history of atopy. Infants respond to bronchodilators such as ipratropium.
Heart failure presents as rapid pulse and liver enlargement and not downward displacement of the liver as in bronchiolitis.
Babies with congenital heart defects, especially those with pulmonary hypertension, may be asymptomatic until they develop bronchiolitis, when they deteriorate rapidly.
Chlamydia trachomatis is uncommon. It usually presents between four and 12 weeks of age. Infants present with cough, tachypnoea and fine crackles on auscultation. Chest X-ray shows widespread pneumonitis.
Babies with bacterial pneumonias look quite sick. Fever is present in a third of infants, a third may have normal temperature and the other third may be hypothermic.
Pulse oximetry is the most reliable method of assessing both the severity of the illness and the oxygen need in bronchiolitis. However, it has limitations as it can be unreliable if there is anaemia or hypothermia. Pulse oximeters are inaccurate once oxygen saturation falls below 80 per cent.
Chest X-ray is only indicated in severe disease, sudden deterioration, if the diagnosis is in doubt or when there is an underlying cardiac or respiratory disorder.
Nasopharyngeal aspirate (NPA) for RSV immunofluorescence is desirable rather than essential. It can also be used to culture other viruses.
Blood tests are not helpful in bronchiolitis. There are concerns about infants developing hyponatraemia (syndrome of inappropriate ADH secretion). However it is uncommon other than in severe disease.
The majority of infants with bronchiolitis will be managed in the community. Severe and some moderate cases will need admission, especially in the presence of risk factors and adverse social circumstances.
It may help to educate parents in looking out for symptoms of deterioration, particularly with feeding and behaviour.
Treatment is mainly symptomatic and supportive, including paracetamol for fever and for pain relief in associated pharyngitis and otitis media.
Careful attention should be given to nutrition and hydration. The infant may benefit from small, frequent feeds during the acute illness.
Current evidence shows only a small, short-term benefit with bronchodilators such as salbutamol. However, there is no difference in admission rates compared with placebo. Ipratropium does not show any short-term benefit.
There is no current evidence to support the use of epinephrine or corticosteroids.
The routine use of antibiotics is not advocated unless there is evidence of secondary bacterial infection. Hospital management includes the use of ribavirin.
There is limited evidence that ribavirin reduces the need for mechanical ventilatory support. There is some evidence to show that it may reduce the incidence of post-RSV bronchiolitis wheeze.
Palivizumab, a monoclonal antibody, has been shown to reduce admission to hospital and to intensive care, compared with placebo or no prophylaxis.
Premature babies and those with chronic lung disease may benefit from monthly injections over four to six months (with the first injection given before the start of the bronchiolitis season).
Most infants make a full recovery within 10 to 14 days, although a cough and wheeze may persist for weeks.
One-third to half of infants develop wheeze with subsequent viral infections (wheezy baby syndrome).
Some children go on to develop asthma, although confounding factors such as smoking, family history, and severity of illness must be considered.
Mechanical ventilation is needed for up to 8 per cent of admitted infants.
Mortality is 3.5 per cent in infants with congenital abnormalities and chronic lung disease. With no underlying pathology it is 0.1 per cent.
Dr Nelson is a freelance GP in Norwich, Norfolk
Risk factors for severe bronchiolitis
- Age younger than six weeks at presentation.
- Preterm infants.
- Lung disease (chronic lung disease, cystic fibrosis).
- Congenital heart disease.
- Immunodeficiency (congenital or acquired).
- Multiple congenital abnormalities.
- Severe neurological disease.