Husband experiences UTI like symptoms after sex?

So sometimes after sex my husband says he experiences UTI like symptoms for about an hour after sex. It's not all the time, he says it's normally if he pees before sex. Then afterwards it burns, and he has the urge to pee without anything being there. He has to drink a couple of glasses of water and then it subsides within an hour or so. It's not everytime though.

Any idea what causes this?