R., my son went through a biting phase when he was 23 months old at daycare. (I think he did pick it up from a child there because about 6 months before he'd been bitten twice in one week.)
My daycare notified me as soon as I picked him up every day that he had bitten (sometimes he'd done it twice a day!). The same thing happened when he was bitten. They do not tell the parents which child is biting/being bitten. My daycare said it was to prevent parents from dealing with it themselves. So I never knew which child bit my son and which children my son was biting.
My son was put in time out and separated. It took a couple of days to figure out that he was biting two girls ... one of which was new and was really attached to my son. (He's an only child, so he's used to playing alone and didn't like how she wanted to play.) Once the triggers were figured out, they were able to work around them and the biting stopped. After two weeks of him not biting, they let him back around the girls and he did fine.
He was not biting at all at home, so I could not enforce this at home. He also would not understand he was doing anything wrong and comprehend going a whole day without biting equals a treat or something of that nature (he's a little developmentally behind).
It did happen the two weeks after we took a week-long family vacation, so I think it was a combination of going back to school after a week away (he has some separation anxiety) and one of the children that started while he was away. But after two weeks it stopped and he never bit again. Actually, he only bit once the first part of that second week, but I'd say it took 2 weeks to get through the phase.
When he was bitten, I was told there really wasn't anything I could do because they were making sure he was separated from the biter at all times (he was never bitten by the same child). After being bitten, he was comforted while the other child was in time out. When he was the biter, we went through the punishments he was given - time outs, put in a high chair during group activities or when there weren't enough teachers to keep a close eye on him, always separated from the child he bit, etc. Had it been happening at home, we would have enforced the same punishment.
Unfortunately, it is a phase that most children in daycare go through from the people I know that have children in daycare and from all the daycare facilities I toured and questioned before selecting one. You just have to make sure the teachers are staying on top of it; that they notify you of everything that's going on (if that child is biting others, the punishments given, how your child is comforted, if there's a reason for the biting, etc.)
I hope this helps ... I didn't mean for it to be so long! But I was horrified when my son started biting. It caused me so much stress that I was scared to pick him up from daycare. I cried almost every day for those two weeks because I felt so useless ... other than talking to him (which he didn't understand), there wasn't anything else I could do but wait it out or try to figure out the triggers.