Tell him ATTC means stay in camp. Coz safer for him- He has
shown a tendency to be ill; hence he needs to be in an enviroment
where there is medical coverage 24/7. The camp is such an
environement. Plus, Army food is very unlikely to upset his
stomach.
So even if he report sick outside, tell him he has to come back to
camp so that his status can be monitored and he can receive the
best possible care. Of course, if he can get himself admitted into
hospital (and wants to pay) then fine. Fair play to him. 
Edit: To up the BS factor (and piss him off more) remind him that
as a member of the SAF, and as a person in whom the SAF has
invested alot of time and money, the SAF has a vested interest in
ensuring a speedy recovery.