A 3-year-old boy is brought to the pediatrician's office because of rhinorrhea and cough. The child's older brother also has symptoms of a cold. The pediatrician suspects a viral infection and recommends supportive therapy. Sputum examination reveals multi-nucleated giant cells. What is the most likely source of infection?
A Respiratory syncytial virus
B Rhinovirus
C Parainfluenza virus
D Influenza virus
E Bordetella pertussis
(A) is correct. Respiratory syncytial virus (RSV) is a RNA virus that causes infected cells to fuse, giving rise to multi-nucleated giant cells or syncytia. RSV is a common cause of upper respiratory infection in children.
Choices (B), (C), and (D) are incorrect. These are all viruses that cause symptoms of the common cold in young children. However, they do not cause fusion of cells to form syncytia.
Choice (E) is incorrect. Bordetella pertussis is not a virus. It is a bacteria that causes "whooping cough" in children and URI symptoms in adults. It does not cause multi-nucleated giant cell formation.
