I think the idea is that if he's not showing any symptoms (fever and all those other early symptoms), then he is not contagious and even if he is infected, he is still in the incubation period.
But they're not letting him go until they do a further diagnosis.
-penny
Because smallpox can only be transmitted from the time of the earliest appearance of rash, early detection of cases and prompt vaccination of all contacts is critical.
Also, an interesting piece of information from an aricle from Fox News:
The researchers cite the last case of naturally occurring smallpox in October 1977 as further evidence of the difficulty for one person to infect others. Of the 161 persons who had contact with the infected person, 12 unvaccinated persons had face-to-face contact. None of the 12 became ill with clinical cases of smallpox.
Unfortunately, there are some around here needlessly trying to scare people. Smallpox is a relatively easy disease to identify, and it is only contagious once the rash appears.