context: Respiratory syncytial virus ( RSV) is a common, and very contagious, virus that infects the respiratory tract of most children before their second birthday. For most babies and young children, the infection causes nothing more than a cold. But for a small percentage, infection with RSV can lead to serious, sometimes life-threatening problems such as pneumonia or bronchiolitis, an inflammation of the small airways of the lungs. RSV infection can cause cold-like symptoms, including a cough and runny nose, which usually last 1 to 2 weeks. When to see a doctor: Call your baby's doctor if you notice any of the following RSV symptoms: A high-pitched whistling or wheezing noise when they breathe Being unusually upset or inactive A cough with yellow, green, or gray mucus Trouble breathing or pauses in their breaths Refusing to breastfeed or bottle-feed Signs of dehydration: lack of tears when crying, little or no urine in their diaper for 6 hours, and cool, dry skin If your baby is very tired, breathes rapidly, or has a blue tint to their lips or fingernails, call 911 or go to the ER immediately. Respiratory syncytial virus spreads through the air, like after a cough or a sneeze, and through direct contact like touching. The chance of a severe infection is highest for: Babies born prematurely Children younger than 2 who were born with heart or lung disease Infants and young children whose immune systems are weakened because of illness or medical treatment Children under 8 to 10 weeks old To diagnose RSV, your child's doctor will probably look at their medical history and do a physical exam, including listening to their lungs. Your doctor might do some tests if your child is very sick or in order to rule out other problems. Tests for RSV include: Blood and urine tests to look for a bacterial infection and make sure your child isn't dehydrated Chest X-rays to look for any signs of pneumonia Tests of material scraped out of your child's nose or mouth Steps you can take to try to avoid and prevent RSV include: Avoid kissing your baby if you have cold symptoms. Clean and disinfect hard surfaces. Don't let anyone smoke around your baby. If possible, keep your baby away from anyone, including siblings, with cold symptoms. Keep your baby away from crowds. Ask people to wash their hands before they touch your baby. Limit the time high-risk babies and young children stay in day care, particularly from late fall to early spring, when RSV is most common. Wash your hands often, especially after contact with anyone who has cold symptoms. There's no vaccine for respiratory syncytial virus. But a medication called palivizumab may prevent RSV infections and protect high-risk babies from serious complications of RSV infection. If your baby is at high risk, your doctor may give them a monthly shot of it during peak RSV season. Although palivizumab may help prevent serious complications of RSV infection, doctors don't use it to treat RSV. No medication treats the virus itself. So caring for a baby with RSV infection involves treating the symptoms and how it affects your baby's respiratory system. Most babies and young children can be cared for at home: Remove sticky nasal fluids with a bulb syringe and saline drops. Use a cool-mist vaporizer to keep the air moist and make breathing easier. Give your little one fluids in small amounts throughout the day. Use non-aspirin fever-reducers such as acetaminophen. Check the label and follow all directions carefully. Babies with more serious cases may need to go to a hospital, where their treatment may include: Oxygen IV fluids Medications to open their airways