Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Respiratory Syncytial Virus

What Is It?

Respiratory syncytial virus (RSV) is one of the viruses that causes the common cold and infections in the upper parts of the respiratory tract. RSV also can cause infection in the lower respiratory tract, such as pneumonia in the lung tissue and bronchiolitis inside the smallest airways (bronchioles) in the lungs.

RSV is spread in secretions when someone with it coughs or sneezes. RSV also can be carried on unwashed hands and on contaminated objects, such as dirty tissues, doorknobs and desktops. It typically enters the body through the eyes, nose or mouth when someone with contaminated fingers touches his or her face or eyes or breathes in droplets.

People who have the greatest risk of serious illness from RSV include:

• Infants, especially those who were born early (premature)

• The elderly

• People of any age with certain types of heart disease, chronic lung disease or weakened immune systems

In the United States, RSV infections cause numerous hospitalizations and thousands of deaths each year, usually between late fall and early spring. The highest rates of serious childhood RSV illness occur in infants under 6 months old. Almost all children have been exposed to RSV by the age of 2, and most do not become dangerously ill. Getting RSV more than once can happen, but infections that follow the first one generally are mild.