Rare Hepatitis transmission in dental office

This story scares me a little: there really wasn't anything obviously done wrong in a dentist's office here in the U.S. when a rare case of patient-to-patient Hepatitis B transmission took place.

Investigators narrowed it down to a 36 year old woman who had several teeth extracted hours before a woman who came in after her ended up infected by the time she went home. Yeah, you're thinking this was some slummy office where they don't follow universal precautions properly, but it wasn't. The investigators have no idea what went wrong, they're just guessing that a spot must have been missed in the cleaning process. After all, the Hepatitis virus can live invisibly for up to a week on a dry surface.

Creepy.