Microbiology 4 months old infant had respiratory distress.It was diagnosed as bronchiolitis. most common cause of this is A Measles B Respiratory syncytial virus C Influenza D Para Influenza virus 💡 Explanation 4 months old infant had respiratory distress.It was diagnosed as bronchiolitis. most common cause of this is ✓ Correct Answer: B. Respiratory syncytial virus