As explained in my original reply, your child is not at risk for catching HIV in day care -- period. The biological reasons for that fact really don't matter. Nobody ever catches HIV this way.
Everybody concerned about catching HIV in the environment asks the drying question. The more blood dries, the more HIV will be inactivated, but there are no hard and fast limits. Anyway, getting even fresh blood in large amounts into the mouth rarely if ever transmits HIV, and whether or not a child is teething is unlikely to make any difference either.
You came here for reassurance. I gave it. Please accept it and move on. That will be all for this thread.
Many thanks. One final question, if my kid put anything in his mouth with blood on it, say 5-10 minutes later so the. blood was at least starting to dry, is there any hiv risk? He has a habit of picking stuff up off the floor and putting it in his mouth, not just at daycare but everywhere we go. I worry as he is just starting to start teething.
Relax. No risk to speak of.
By regulations that apply in most if not all states, day care facilities are supposed to be on the lookout to prevent blood-borne infections like hepatitis B and HIV, primarily by preventing injuries and, if one occurs, properly cleaning up any blood before other kids are at risk. Fortunately, such infections are rarely if ever transmitted by biting, and not through saliva and other body secretions. (Even swallowing HIV infected blood carries little risk.) The risk is also low because there are so few HIV infected young kids in the US these days. I'll bet there has not been a single case of HIV in a child acquired in day care in the US in the past 10 years.
There are, of course, real infection risks in day care, or in any other setting where young children are placed together in signficant numbers. You can be sure your child will catch colds and norovirus (the main cause of 1-2 day bouts of vomiting and diarrhea) in day care, probably a couple times a year if not more. Tuberculosis, hepatitis A, strep throats, influenza, molluscum congatiosum, herpes due to HSV-1, all the common childhood diseases, and a number of others all are more frequent in such children -- and in their family members at home -- than in kids who don't go to day care. Day care facilities in most if not all states operate under regulations that require standard precautions to attempt to reduce these risks, and known infected kids are to be kept at home. But as you can imagine, these measures reduce but do not eliminate the risks.
For all these reasons, feel free to discuss infection control with day care manager. Be on the lookout for all the garden variety infections. But don't worry about your child catching HIV. (And by the way, don't ask whether there are any HIV infected kids attending. They won't know, and if they do, it is against the law to reveal it.)
I hope this helps. Best wishes-- HHH, MD