Summed up perfectly by Direct Anywhere's Post #46. What people outside of aviation do not understand is that you cannot fly if you have a cold/URTI due to ears blocking/possible damage to eardrums etc. At your office desk, no problem, and most people will push on through. Go flying and possibly perforate an eardrum or two, and the person will be off for a very long time compared to the time required to come right. There is also the lesser known possibility of causing brain damage from flying with a cold and ending up being permanently out of the job. In flying, outside of injuries, the common cold/URTI's would account for the majority of sick leave taken. The other "gotcha" occurs from the environment itself - breathing the recirculated air all day lomg from hundreds of passengers, a lot of whom are carrying the "bugs" adds insult to injury and contributes to a greater incidence of picking up these infections in the work environment. I would suspect that crew on solely freight operations wouldn't develop as many colds etc during the course of a year as what pilots carrying passengers pick up.