well the tension ur friend going through can only be imagined its really hard..............i have seen many in my career some go through severe depression anyway 1st of all best of luck for him any undue things wont happen to him secondly like some1 rightly said he can take the sex worker 4 hiv test but i dont know how far is that feasible many a times such workers r untraceable seconly if u r so much worried u can go for p24 test to rule out hiv in ur blood p24 testing may be used to detect early HIV infection and to screen donated blood for HIV. The p24 test is one of the earlier tests developed to detect HIV infection..... n more than that matter isnt that of hiv alone there r many other sti(sexually transmitted infection)which should be taken care of........