Human respiratory syncytial virus (RSV) is a negative-sense, single-stranded RNA virus of the family Paramyxoviridae, which includes common respiratory viruses such as those causing measles and mumps. RSV is a member of the paramyxovirus subfamily Pneumovirinae.
RSV causes respiratory tract infections in patients of all ages. It is the major cause of lower respiratory tract infection during infancy and childhood. In temperate climates there is an annual epidemic during the winter months. In tropical climates, infection is most common during the rainy season. In the United States, 60% of infants are infected during their first RSV season[citation needed], and nearly all children will have been infected with the virus by 2-3 years of age[citation needed]. Natural infection with RSV does not induce protective immunity, and thus people can be infected multiple times. Sometimes an infant can become symptomatically infected more than once even within a single RSV season. More recently, severe RSV infections have increasingly been found among elderly patients as well.
For most people, RSV produces only mild symptoms, often indistinguishable from common colds and minor illnesses. The Centers for Disease Control consider RSV to be the "most common cause of bronchiolitis and pneumonia among infants and children under 1 year of age."[1] For some children, RSV can cause bronchiolitis, leading to severe respiratory illness requiring hospitalization and, rarely, causing death. This is more likely to occur in patients that are immunocompromised or infants born prematurely. Other RSV symptoms common among infants include listlessness, poor or diminished appetite, and a possible fever.[1].
Recurrent wheezing and asthma are more common among individuals who suffered severe RSV infection during the first few months of life than among controls; whether RSV infection sets up a process that leads to recurrent wheezing or whether those already predisposed to asthma are more likely to become severely ill with RSV is a matter of considerable debate.
