I recently found out that my cousin has had HIV for the past seven years. We used to own a nail salon together and were really close. We shared many things -- sandwiches, sodas and cigarettes. I also manicured her nails for her and then used the same file on myself and others. Do I have anything to be worried about?

L.

This is a very common concern: "I have a friend who has HIV. Can I catch it?" Fortunately, the short answer is no -- you have nothing to worry about. That said, let me try to explain some of the particulars. HIV (human immunodeficiency virus, the virus that causes AIDS) is not particularly contagious. The vast majority of cases of HIV result from either sexual transmission, intravenous drug use, blood transfusion (mostly before 1985) or transmission from mother to child around the time of delivery.

Some other potential methods of transmission could concern you. For example, there have been reported cases of the virus being spread within a household. Most of these cases involve sexual transmission. In some, the means of spread was apparently through more-casual contact -- perhaps through biting, sharing a toothbrush or something similar. However, these cases are very rare, so we generally do not have to worry about such unusual modes of spread. (It's important to realize that HIV does not survive for long on objects. Simply drying in the air lowers the infectivity of the virus substantially.) This is what I tell my patients with HIV: It is rare for the virus to be transmitted through the sharing of household items. However, it is probably not prudent to share intimate items such as toothbrushes with others.

I have heard concerns about the transmission of HIV through razors at the barbershop or through nail manicuring. However, according to the U.S. Centers for Disease Control (CDC), there have been no documented cases of transmission in this way. The CDC recommends that items designed to pierce the skin, such as those used in tattooing or body piercing, be used only once or thoroughly sterilized between uses. Items not designed to penetrate the skin that may nonetheless become contaminated with blood, such as razors or manicuring instruments, should also be used only once or thoroughly disinfected between uses. Again, I want to stress that transmission by these means would be very rare and that no such cases have been reported.