What is RSV?

This is a question about an infant who is just three months old. The baby was hospitalized after having what appeared to be a cold or congestion. The baby was diagnosed as having some condition of the bronchioles, and it was determined to be a virus called RSV. The baby fortunately is better and out of the hospital, but I am curious as to what this virus was?
Utica, New York

Dr. Greene’s Answer:

RSV, or Respiratory Syncytial Virus, is the most important respiratory organism of early childhood. It occurs throughout the world, and in each location it tends to occur in yearly winter outbreaks. In the northern hemisphere the peak of the epidemic is usually in January, February, or March, although in some years it may begin earlier and/or end later. Each year, around 100,000 infants are hospitalized with RSV in the United States alone. This year the epidemic has been particularly heavy (even in sunny California). The last several months have seen many, many children hospitalized with RSV.

The virus lives inside the cells lining the respiratory system, causing swelling of this lining coupled with the production of large amounts of excess mucus. In adults, this shows up as a bad, lingering cold with thick nasal congestion and a deep, productive cough. In infants, however, the excess mucus can be enough to plug their small airways or bronchioles, resulting in a severe illness called bronchiolitis that requires hospitalization.


The time period from exposure to illness is usually about 4 days. Typically a parent, or more likely an older sibling, comes down with a bad cold first. The disease spreads when infected droplets in the air or on the hands comes into contact with the baby’s mouth or nose (It has never been shown to be passed from someone standing as far as 6 feet away). Then, the infant develops a runny nose and a red throat. Over the next 3 days or so the infant gets sicker. Symptoms include cough, wheezing, and sometimes a fever or an ear infection. In most infants, this is as severe as RSV gets. Some, though, will get progressively sicker with fast respirations (>60 per minute), difficulty breathing, and listlessness. About 3% of infected infants get sick enough to require hospitalization. The disease usually lasts 5 to 12 days.

The best way to prevent RSV is good hand washing, particularly just before handling susceptible infants. Use a tissue when you cough or sneeze. If possible, avoid exposure to sick individuals during the peak of RSV season.

Although those who have been infected develop some antibodies to RSV, most individuals are susceptible again by the next annual outbreak. Subsequent infections, though, are usually both less common and much less severe. Only about 15% of children over the age of 2 will have a case of RSV in each epidemic.


A study in the January 2000 issue of Pediatrics describes a simple blood test that can predict which children are most likely to go on and develop asthma. The study looked at children sick enough to be hospitalized with RSV. Those who had a high eosinophil count had a 56% chance of developing asthma. The others with severe RSV had only a 22% chance. While RSV and asthma certainly go together, even with severe RSV and a high eosinophil count, there is a good chance of avoiding asthma altogether.

It is not known whether the virus damages the respiratory system thus causing the asthma, or if people’s susceptibility to asthma predisposes them to severe RSV. I suspect that it is a little of both.

I am very glad that your 3-month-old is doing better. I would recommend avoiding respiratory irritants (such as cigarette smoke), and ensuring good nutrition (particularly vitamin A — which is thought to have a healing effect on the respiratory lining). This long winter is finally nearing the end, and by the time the next epidemic hits, that little one will be at an age to run across the room to you and give you a great, big hug!

Update: Two products are now available to prevent RSV infection in children at high risk for serious disease. RSV-IGIV (RespiGam) and palivizumab (Synagis) have been approved for children younger than 24 months with chronic lung disease/bronchopulmonary dysplasia or a history of premature birth (< 35 weeks).

Dr. Alan Greene


  1. Alyssa

    I have been babysitting a child and just found out he has rsv. I was wondering how likely it is for my six year old to catch it.


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