Respiratory syncytial virus
Respiratory syncytial virus (RSV),[a] also called human respiratory syncytial virus (hRSV) and human orthopneumovirus, is a contagious virus that causes infections of the respiratory tract. It is a negative-sense, single-stranded RNA virus.[2] Its name is derived from the large cells known as syncytia that form when infected cells fuse.[2][3]
RSV is a common cause of respiratory hospitalization in infants, and reinfection remains common in later life though often with less severity. It is a notable pathogen in all age groups. Infection rates are typically higher during the cold winter months, causing bronchiolitis in infants, common colds in adults, and more serious respiratory illnesses, such as pneumonia, in the elderly and immunocompromised.[4]
RSV can cause outbreaks both in the community and in hospital settings. Following initial infection via the eyes or nose, the virus infects the epithelial cells of the upper and lower airway, causing inflammation, cell damage, and airway obstruction.[2] A variety of methods are available for viral detection and diagnosis of RSV including antigen testing, molecular testing, and viral culture.[3]
The main recommended prevention measures include hand-washing and avoiding close contact with infected individuals.[5] The detection of RSV in respiratory aerosols,[6] along with the production of fine and ultrafine aerosols during normal breathing, talking,[7] and coughing,[8] and the emerging scientific consensus around transmission of all respiratory infections,[9] airborne precautions may also be required for reliable protection. In May 2023, the US Food and Drug Administration (FDA) approved the first RSV vaccines, Arexvy (developed by GSK plc) and Abrysvo (Pfizer).[10][11] The prophylactic use of palivizumab or nirsevimab (both are monoclonal antibody treatments) can prevent RSV infection in high-risk infants.[5][12]
Treatment for severe illness is primarily supportive, including oxygen therapy and more advanced breathing support with continuous positive airway pressure (CPAP) or nasal high flow oxygen, as required. In cases of severe respiratory failure, intubation and mechanical ventilation may be required. Ribavirin is an antiviral medication licensed for the treatment of RSV in children.[13] RSV infection is usually not serious, but it can be a significant cause of morbidity and mortality in infants and in adults, particularly the elderly and those with underlying heart or lung diseases.
History[edit]
RSV was discovered in 1956 when researchers isolated a virus from a population of chimpanzees with respiratory illness. They named the virus chimpanzee coryza agent (CCA).[14] In 1957, this same virus was identified by Robert M. Chanock in children with respiratory illness.[15] Studies of human antibodies in infants and children revealed that the infection was common in early life.[16] The virus was later renamed human orthopneumovirus, or human respiratory syncytial virus (hRSV).[17][18]
Several other pneumoviruses show great similarity to hRSV. Bovine RSV (bRSV) shares approximately 80% of its genome with hRSV. It also shares hRSV's predilection for the young, causing more severe disease in calves less than six months old. Because bRSV-infected calves have almost identical symptoms to hRSV-infected children, they have proven to be an important animal model in RSV research.[19]
Mechanism[edit]
Transmission[edit]
RSV is highly contagious and can cause outbreaks from both community and hospital transmission.[3] For each person infected with RSV, it is estimated that an average of 5 to 25 uninfected people will become infected.[36] RSV can spread when an infected person coughs or sneezes, releasing contaminated droplets into the air. Transmission usually occurs when these droplets come into contact with another person's eyes, nose, or mouth.[37] As with all respiratory pathogens once presumed to transmit via respiratory droplets, it is highly likely to be carried by the aerosols generated during routine breathing, talking, and even singing.[9] RSV can also live for up to 25 minutes on contaminated skin (i.e. hands) and several hours on other surfaces like countertops and doorknobs.[3][36] It has an incubation period of 2 to 8 days.[3] Once infected, people are usually contagious for 3 to 8 days. In infants and in people with weakened immune systems, however, the virus may continue to spread for up to 4 weeks (even after they are no longer showing symptoms).[37]
Diagnosis[edit]
Laboratory diagnosis[edit]
A variety of laboratory tests are available for the diagnosis of RSV infection. While the American Academy of Pediatrics (AAP) does not routinely recommend the use of lab testing to diagnose RSV bronchiolitis (for which the treatment is largely supportive),[5] confirmation of RSV infection may be warranted in high-risk groups if the result will guide clinical decisions. Common identification techniques include antigen testing, molecular testing, and viral culture.[3]
Prevention[edit]
General prevention measures[edit]
The main prevention measure is to avoid close contact with infected individuals.[5] Airborne precautions such as respirators, ventilation, and HEPA/high MERV filters, are likely protective against RSV-laden aerosols.[9]
Treatment[edit]
Supportive care[edit]
Treatment for RSV infection is focused primarily on supportive care. This may include monitoring a patient's breathing or using suction to remove secretions from the upper airway. Supplemental oxygen may also be delivered though a nasal cannula or face mask in order to improve airflow. In severe cases of respiratory failure, intubation and mechanical ventilation may be required to support breathing. If signs of dehydration are present, fluids may also be given orally or through an IV.[45]
Additional supportive treatments have been investigated in infants hospitalized with RSV bronchiolitis. These include:
Epidemiology[edit]
Infants and children[edit]
Worldwide, RSV is the leading cause of bronchiolitis and pneumonia in infants and children under the age of 5. The risk of serious infection is highest during the first 6 months of life. Of those infected with RSV, 2–3% will develop bronchiolitis, necessitating hospitalization.[63] Each year, approximately 30 million acute respiratory illnesses and over 60,000 childhood deaths are caused by RSV worldwide. An estimated 87% of infants will have experienced an RSV infection by the age of 18 months, and nearly all children will have been infected by 3 years. In the United States, RSV is responsible for up to 20% of acute respiratory infection hospitalizations in children under the age of 5. However, the vast majority of RSV-related deaths occur in low-income countries that lack access to basic supportive care.[3]
Adults[edit]
It is rare for healthy young adults to develop severe illness requiring hospitalization from RSV. However, it is now recognized as a significant cause of morbidity and mortality in certain adult populations, including the elderly and those with underlying heart or lung diseases. Its clinical impact among elderly adults is estimated to be similar to that of influenza.[26] Each year, approximately 5–10% of nursing home residents will experience RSV infection, with significant rates of pneumonia and death. RSV is also responsible for 2–5% of adult community-acquired pneumonias.[26]
Immunocompromised[edit]
In both adults and children, immunosuppression increases susceptibility to RSV infection. Children living with HIV are more likely to develop acute illness, and are 3.5 times more likely to require hospitalization than children without HIV.[3] Bone marrow transplant patients prior to marrow engraftment are at particularly high risk, with RSV accounting for nearly half of the viral infections in this population. This group has also demonstrated mortality rates of up to 80% among those with RSV pneumonia.[26] While infection may occur within the community, hospital-acquired infection is thought to account for 30–50% of cases among immunocompromised individuals.[26]
Seasonality[edit]
RSV seasonality varies around the world. In temperate climates, infection rates tend to be highest during the cold winter months. This is often attributed to increased indoor crowding and increased viral stability in the lower temperatures. In tropical and arctic climates, however, the annual variation is less well defined and seems to be more prevalent during the rainy season.[2][3] Annual epidemics are generally caused by the presence of several different viral strains. Subtype A and B viruses will often circulate simultaneously within a specific geographic region, although group A viruses are more prevalent.[26]