The sad thing about this sort of thing is this: IT'S ABSOLUTELY PREVENTABLE! All it takes is a little bit of care by the surgeon(s) and the support staff; all of which share blame for this sort of thing generally. A surgeon, however, should share the lion's share of the blame tough.
This sort of thing, which happens regularly, is known as a "Never Event" because it should never happen. However, a lot of surgeons are being encouraged by their malpractice insurance carriers to call sewing up a sponge in a patient (which the surgeon did) a "Hospital Acquired Condition." Why? Because it makes it look like it's something the hospital alone did wrong and not the surgeon. This is when you really need to be concerned---as a patient---that your surgeon, if he or she sews a sponge up in you during surgery, will refuse to accept responsibility and pawn it off on the hospital as a "Hospital Acquired Condition." Is that really the "right thing to do"?