Infants and children Worldwide,<unk>  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<unk> , 2–3% will develop bronchiolitis, necessitating hospitalization. Each year, approximately 30 million acute<unk>  illnesses and over 60,000 childhood deaths are caused by<unk>  worldwide. An estimated 87% of infants will have experienced an<unk>  infection by the age of 18 months, and nearly all children will have been infected by 3 years. In the United States,<unk>  is responsible for up to 20% of acute<unk>  infection hospitalizations in children under the age of 5. However, the vast majority of<unk> -related deaths occur in low-income countries that lack access to basic supportive care. Adults It is rare for healthy young adults to develop severe illness requiring hospitalization from<unk> . 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. Each year, approximately 5-10% of nursing home residents will experience<unk>  infection, with significant rates of pneumonia and death.<unk>  is also responsible for 2-5% of adult community-acquired pneumonias. Immunocompromised In both adults and children, immunosuppression increases susceptibility to<unk>  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. Bone marrow transplant patients prior to marrow engraftment are at particularly high risk, with<unk>  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<unk>  pneumonia. While infection may occur within the community, hospital-acquired infection is thought to account for 30-50% of cases among immunocompromised individuals. Seasonality<unk>  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. 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. COVID-19 The COVID-19 pandemic resulted in a significant decline in the prevalence of<unk> . There was then a significant unseasonal rebound when lockdowns and other restrictive measures were relaxed.
Respiratory syncytial virus
Influenza A virus
Influenza B virus
Influenza D virus
Rhinovirus
Human parainfluenza viruses
Human coronavirus 229E
Cricket paralysis virus