Which factors can contribute to the

spread of viruses?

Weak immune system, and lots of contact like one person coughs in and elevator you have a chance of getting the cold because your exposed to the bacteria through the air.

precipitation, humidity wet hot environment,

the number of people with whom an infected person comes in contact; and,

Answer: Virus transmission is affected by a number of factors, including environmental determinants, host behavior, host defense mechanisms, and virus infectivity. Uncertainties remain with respect to the relative importance of these factors and the roles that they play.