Influenza virus is most likely to leave a host through this portal of exit:

Influenza is an infection caused by an influenza virus (RNA virus).
There are four types of influenza viruses: A, B, C and D.  A and B are the most common flues, C causes respiratory illness an D primarily affect cattle.
Influenza is an enveloped virus.  It uses the host cell's plasma membrane to form the viral particles that leave the cell and go on to infect neighboring cells.

That statement is false

Because In determining body composition, the doctors also have to measure the amount Muscles, Bones, and water in our body

But since muscle and water takes up less space in our body, the amount of fat really determine our body frame