I found one of my roommmates using my toothbrush recently, and I'm sure it wasnt the first time. I just had an HIV test and it was negative, however I'm unsure of their status, although I know they have been in a steady relationship for almost 2 years. My question is my gums bleed so should I be concerned about getting something from them??? How high are the risks? Since they've probably used it before and we've been living together for a year, should I just assume it was accounted for on the last test?
Even if your roomate is infected with HIV, it is highly unlikely that HIV would be transmitted to you by sharing a toothbrush. Transmission through sharing a toothbrush is not a likely event; there is no actual evidence that HIV has been transmitted this way. One explanation for this could be that HIV does not survive in the environment long (see http://www.thebody.com/cdc/survival.html).
HIV is spread in three main ways: sexual contact, blood-to-blood contact (usually sharing injection needles), and mother-to-infant.
It is recommended that one does not share the toothbrush or razor of an infected person because blood left on the objects could transmit HIV. These recommendations exist as a precaution primarily for those living or having contact with HIV infected individuals.