IF what you saw was oral or nasal sputum, then really there is little or nothing for you to worry about, especially as you were meticulous about avoiding direct contact with it. However, from the description it would seem highly unlikely. Far more likely would be a residual discharge from the anus from someone with an infection. I would stress that the infection symptoms are NOT necessarily indicative of AIDS. Anyone with any one of a number of infections of the digestive tract might leave such a trace. As has already been stated, if the residue contained traces of blood, and it was HIV infected blood, then theoretically an open cut or skin abrasion might allow an infection to enter your body. But the odds are astronomically small, particularly if you observe post-toilet hygiene.
I wouldn't worry if I were you. If this continues to haunt you, then go to a Sex Clinic and claim that you have had unprotected sex, and need testing for HIV. That at least should put your mind at rest.
