Bronchiolitis
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Direct answer
Bronchiolitis is an acute viral lower respiratory infection of the bronchioles, predominantly caused by respiratory syncytial virus (RSV), affecting children under two years with a peak around two to six months. Its hallmark is the first wheezing episode of an infant: coryza for a few days, then cough, tachypnoea, diffuse wheeze and crepitations with hyperinflation and feeding difficulty. Management is supportive — hydration and oxygenation, with ventilatory support for the few who deteriorate — since bronchodilators, steroids, antibiotics and physiotherapy are not routinely beneficial.
What you must remember
- Cause: respiratory syncytial virus in most cases; human metapneumovirus, parainfluenza, rhinovirus, adenovirus and bocavirus account for the rest, with winter epidemics.
- High-risk infants: prematurity, chronic lung disease, congenital heart disease with increased pulmonary blood flow, immunodeficiency, age under three months and passive smoke exposure; apnoea may be the presenting sign in very young or preterm infants.
- Pathophysiology: viral inflammation and epithelial necrosis of small airways with mucus and oedema produce obstruction, air trapping, atelectasis and hyperinflation — hence the prolonged expiratory phase.
- Clinical picture: coryzal prodrome, then tachypnoea, recessions, nasal flaring, widespread fine crepitations with expiratory wheeze and poor feeding; hypoxaemia, not wheeze loudness, defines severity.
- Investigations: diagnosis is clinical; chest radiograph (hyperinflation, perihilar markings, patchy atelectasis) and viral testing are reserved for atypical or severe disease; pulse oximetry is the key monitor.
- Treatment: supportive — oxygen targeting saturations of about 90 per cent or above, nasal suction, and hydration by tube or intravenous fluids when feeding fails; bronchodilator trials only if objectively helpful; corticosteroids, antibiotics, physiotherapy and ribavirin are not routine (ribavirin only for the severely immunocompromised).
- Prevention: hand hygiene and smoke avoidance for all; passive immunisation of high-risk infants — monthly palivizumab historically, now joined by single-dose long-acting monoclonal antibody and maternal vaccination in several countries.
Common confusion
Bronchiolitis is confused with a first asthma attack and with pneumonia. The bronchiolitis infant is under a year (usually under six months), in winter, with a first wheeze and viral prodrome, and typically fails to respond to bronchodilators — which itself argues for bronchiolitis over reactive airway disease. Pneumonia shows focal crepitations with high fever rather than diffuse symmetrical wheeze with hyperinflation. A third trap is deterioration timing: illness worsens over the first days before improving over one to two weeks, so the day-four feeding assessment matters.
Exam-focused takeaway
NEET-PG tests bronchiolitis as a "what not to do" subject: the baby under six months with first wheeze receives oxygen, hydration and suction — not steroids, not routine antibiotics, not physiotherapy. Vignettes ask the next best step in a wheezing infant with poor feeding (assess saturation and hydration), the causative virus, and the high-risk features lowering the admission threshold. Prevention questions now include nirsevimab and maternal RSV vaccination alongside palivizumab.
Frequently asked questions
What causes bronchiolitis?
Respiratory syncytial virus in the large majority, with human metapneumovirus, parainfluenza, rhinovirus and adenovirus accounting for the rest.
Why are bronchodilators and steroids not routine?
Trials show no consistent benefit — the disease is bronchiolar obstruction with debris and oedema, not bronchospasm these drugs reverse; a bronchodilator trial continues only if the infant responds objectively.
When does an infant need admission?
For persistent hypoxaemia (around 90 per cent or below), poor feeding, apnoea, high-risk background, or when parents cannot monitor.
Can bronchiolitis be prevented?
Partly — hygiene and smoke avoidance for all infants, plus passive immunisation for high-risk groups: monthly palivizumab, and newer options including single-dose long-acting monoclonal antibody and maternal vaccination.
Can it present with apnoea?
Yes, especially in very young or preterm infants — apnoea may precede respiratory signs and is itself an indication for admission.