Tom is 7 months old and is brought to the GP surgery by his concerned father. He is worried that he has a fever of 38°C, has been wheezy and had a dry cough and runny nose over the last few days. He is usually a happy child, is up to date with immunisations and has no other medical problems. He is maintaining most of his usual oral intake.
On examination, his respiratory rate is 40 but other observations are normal and diffuse bilateral wheeze and crackles are noted on chest auscultation.
What is the most likely diagnosis?