INTRODUCTION
Bronchiolitis is defined by IAP as ’ A constellation of clinical symptoms and signs including viral upper respiratory prodrome followed by increased respiratory effort and wheeze in less than 2 year old children’. Many virus cause bronchiolitis with Respiratory syncytial virus being common. Epidemiology of RSV has many unusual characteristics. They infect children nearly in first year of life with the peak incidence in 2 – 8 months. Its is the only virus which cause most severe respiratory disease in the first month of life when there is antibodies from the mother.1 WHO estimated RSV burden globally as 64 million cases and 1,50,000 deaths every year. Peak incidence at 2-8 months of age. This is one of the common cause of hospitalisation
Intensive care is needed for about 15% to 30% of RSV infections. Due to respiratory failure , apnoea 7% to 21% of hospitalised patient needs mechanical ventilation 2 . Some prospective study have suggested that RSV infection predisposes to blood eosinophilia and airway hyperreactivity leading to development of wheeze
Overproduction of cytokines released by helper 2 T lymphocytes is responsible for illness especially interleukin 4 and 5. These are responsible for wheeze.Interleukin 4 and 5 cause migration of eosinophil and also increases IgE production. 3