Studies have been done for many years about living in a household with someone who has HIV.  As mentioned, many of the times there will be a mother and a father and some children.  One, let's say the father, has HIV, and becomes ill.  He's become ill but before he became ill, he had HIV, sometimes for several years. What happens to the people who are not his sexual partners?  What happens to the aunt, or the grandmother, or the sibling of the infected person?  What is their risk from living in the household, from sharing food, sharing drinking glasses, sharing utensils, sharing a toilet, just being around, watching them just in general life in a family setting?  Well, testing has been done on the family members and the relatives who live with the affected people who have HIV and, even in crowded quarters in low-income areas in New York City, no one was affected with HIV, or infected with HIV, who did not already get it on their own.  In other words, there might be a person who was out shooting drugs and got his own HIV infection even though he lived in the household with his older brother who got HIV separately.  But there was no transmission from parent to child, from sibling to sibling, from older generation to younger generation that wasn't otherwise done of independently catching a virus.  In other words, it didn't matter if they shared a toothbrush in almost all instances.  There's one case, maybe, in Germany of getting HIV by sharing a razor from an infected brother to the non-infected brother.  It's possible, and I certainly wouldn't recommend people share razors.  But the point is, it's pretty hard to catch HIV unless one engages in the risk behaviors.