Brochiolitis a Brochiolitis is the most common serious respiratory infection of infancy. Two to three per cent of all infants are admitted to hospital with the disease each year during annual winter epidemics. ninety per cent are aged 1-9 months brochiolitis is rare after one year old. Respiratory syncitial virus (RSV is the pathogen in 75-80%casesBrochiolitis ◼ Brochiolitis is the most common serious respiratory infection of infancy. Two to three per cent of all infants are admitted to hospital with the disease each year during annual winter epidemics. Ninety per cent are aged 1-9 months brochiolitis is rare after one year old. Respiratory syncitial virus (RSV) is the pathogen in 75-80% cases