Transmission<unk>  is highly contagious and can cause outbreaks from both community and hospital transmission. For each person infected with<unk> , it is estimated that an average of 5 to 25 uninfected people will become infected.<unk>  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.<unk>  can also live for up to 25 minutes on contaminated skin (i.e. hands) and several hours on other surfaces like countertops and doorknobs. It has an incubation period of 2 to 8 days. 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). Lumen of an obstructed bronchiole containing cellular debris and aggregates of sloughed epithelial cells Pathogenesis Following transmission through the nose or eyes,<unk>  infects ciliated columnar epithelial cells of the upper and lower airway.<unk>  continues to replicate within these bronchial cells for about 8 days. After the first several days,<unk> -infected cells will become more rounded and ultimately slough into the smaller bronchioles of the lower airway. This sloughing mechanism is also thought to be responsible for the spread of virus from the upper to lower<unk>  tract. Infection causes generalized inflammation within the lungs, including the migration and infiltration of inflammatory cells (such as monocytes and T-cells), necrosis of the epithelial cell wall, edema, and increased mucous production. Inflammation and cell damage tends to be patchy rather than diffuse. Together, the sloughed epithelial cells, mucous plugs, and accumulated immune cells cause obstruction of the lower airway.
Respiratory syncytial virus
Influenza A virus
Influenza B virus
Influenza D virus
Rhinovirus
Human parainfluenza viruses
Human coronavirus 229E
Cricket paralysis virus