Literature

Literature search is divided with regards to the factors determining or influencing the infectivity of the influenza virus.

Known factors determining the infectivity of the virus

1. constituents of nasal secretions (e.g. mucus present or no)
2. type of the surface (smooth or porous), on which the virus was deposited; smooth surface enhances virus spread
3. virus type
4. virus concentration
5. temperature
6. relative humidity (RH)
7. exposition to light and UV
8. pH

Possible routes of infection

1. large droplets (10-20 $\mu$ in diameter)
2. aerosol (small droplets of diameter < 5 $\mu$; aerosols are the source of long-range infections; it seems, that aerosols are the main route of infection)
3. direct contact

Particles of diameter < 3 $\mu$ basically do not settle, particles of diameter 5 $\mu$ settle after ~62 min, and those of diameter 100 $\mu$ settle after 10 s. There is a notion of droplet nucleous, which is a shrunken by evaporation droplet coming from a sneeze or a cough. Initially it have around 20 $\mu$ diameter but it can shrink twice by evaporation. Such droplet nuclei are highly higroscopic. Most sneeze or cough droplets have diameter < 5-10 $\mu$.

Factors influencing long-range infections

1. concentration
2. infectious dose
3. the number of infectious particles produced
4. the duration of shedding by infected carrier
5. the stability of the carrier in the environment