Respiratory syncytial virus, or RSV, is a virus that attacks the mucous membranes of people's respiratory tracts (the nose, throat, windpipe, and the bronchi and bronchioles (the air passages of the lungs). (The term syncytial means that the virus causes cells -- in this case, cells of the mucous membranes -- to merge together into larger cells which, however, don't work as well as the original non-infected cells.) The virus only infects humans.
In older children and adults, RSV usually causes very bad colds with lots of clear nasal drainage, but it can also cause laryngitis and bronchitis, and can trigger or worsen attacks if you happen to have asthma or other chronic lung problems. Since you do not stay completely immune to RSV for life once you have had it, you can get it again and transmit it to other people as well. It usually takes 2 to 8 days after you are exposed to RSV before you become sick. Once you have RSV you will likely shed RSV particles for 3 to 8 days, but small infants who have been infected may be contagious for up to 4 weeks.
In small infants RSV also causes mucus membrane damage and clear drainage. However, because babies and their air passages are small, an RSV infection can clog up the air passages much more easily. RSV bronchiolitis (inflammation of the small air passages) and RSV pneumonia are very common during the season (usually in the winter and early spring -- I myself admitted six babies to the hospital with RSV in two days over Thanksgiving weekend, 1997). Babies with RSV cough a lot -- sometimes the cough sounds just like that of whooping cough -- and can have trouble getting enough oxygen if the infection is bad enough. Babies born prematurely, especially those with lasting breathing problems, are especially likely to have severe problems with RSV.
There are several ways to test for RSV. We can grow the virus in cultured cells, or we can look for antibodies to the virus in a patient's blood (although we have to take two or more sample days or weeks apart and show that the RSV antibodies have increased). We can also use antigen-antibody tests to look for the virus: these tests give results in hours, but are not as accurate as the culture and blood antibody tests.
We do not yet have a vaccine that protects against RSV. However, we have immune globulins that will give temporary immunity to patients, and that we give to children (such as babies born prematurely) who are most likely to have life-threatening RSV infections. The best prevention involves good handwashing, and keeping small babies away from anyone known to have RSV (and possibly even from anyone with a bad cold).
Since RSV is a virus, the antibacterial antibiotics will not help at all, although they might be needed for a child who gets a bacterial infection on top of an RSV infection. Unlike most viruses, there is a medicine, ribavirin, which can block RSV infections. There are many problems with ribavirin: it must be inhaled, so a patient on ribavirin must be in a mist or oxygen tent or on a ventilator, and it is known to cause birth defects in animals (it has not been proven that people are at risk, but if you are pregnant you should be nowhere near a hospital room where ribavirin is being given). These days, hardly anyone resorts to ribavirin for treatment of RSV.
We also now have available immune globulin specifically for RSV. These come in two forms: an immune globulin produced from patients who have had RSV and are now immune to it, and another that is produced by recombinant DNA technology. The recombinant immune globulin can be given by your child's doctor in the office; the other form must be given through an IV, and is usually given only in the hospital. These immune globulins can be given to patients who are particularly at risk for RSV, such as premature babies. Unfortunately the RSV immune globulin needs to be given every month during the RSV season. In severe cases we may give RSV immune globulin to a baby with active RSV if she is due for a dose anyway, since that can help her get rid of the virus faster. Your doctor can give you more details, and help you determine whether this is a good idea for your child.