Final answer:
RSV is a virus that can cause respiratory tract infections, including pneumonia. It is common in infants and can be life-threatening.
Step-by-step explanation:
Viruses can cause respiratory tract infections, including pneumonia. One such virus is the Respiratory Syncytial Virus (RSV). RSV infections are common in infants and can be life-threatening. In adults, RSV infections are usually self-limiting and resolve within 1 or 2 weeks.