Boston ? Jesica Santillan passed the point of no return at precisely 4:50 p.m. on Feb. 7. This was the moment when the surgeon cut open the chest of the 17-year-old and removed her heart and lungs.

It’s hard to overstate the drama of that moment in any heart transplant, let alone this one. After all, Jesica had been smuggled into this country from a small town in Mexico by parents intent on saving her life. She had waited three years at the gates of the “City of Medicine,” as Durham, N.C., is pridefully labeled, for a new heart, new lungs and a new lease on life.

But that day, all the surgical skill, all the training, all the high-tech machinery and experience at her service in the Duke University Medical Center was undone by a mistake as basic as the alphabet. Jesica, who had type O blood, was given organs from someone with type A.

Somewhere along the line, the people at the organ bank and the doctor each assumed the other had matched the blood type. Nobody cross-checked. So began the cascade of disasters — organ rejection, a second transplant, brain damage — that ended in death.

It wasn’t the hands of the surgeon that slipped or the machinery that broke down. In the operating room, a shrine to cutting-edge medicine, Jesica Santillan became a victim of error, not evil. She became proof of what Donald Berwick, a watchdog of medical mistakes, calls “the banality of screw-up.”

What then are we to make of her death, besides cause for mourning? A cashier in a local gas station in nearby Louisburg, N.C., said, “I know everybody makes mistakes. We are human. But that doesn’t bring her back.” Precisely. If you confuse an O with an A in my business, you run a correction. Confuse it in medicine and you may run an obit.

Jesica was by no means the first time we confronted a medical mistake. In 1995, I lost a colleague to an overdose of anti-cancer medicine. In the last seven years, at least 150 patients have had the wrong leg, arm, breast or some other body part removed.

A few years ago, the Institute of Medicine published a report on medical mistakes they called “To Err is Human.” It said that 44,000 to 98,000 people died every year from medical mistakes — more than die from car accidents or breast cancer or AIDS.

Most mistakes are not the result of incompetent or uncommitted doctors, nurses or pharmacists. Ask the devastated team at Duke. They are, rather, the result of a failure of a system, the failure to build what Berwick calls “dikes” against inevitable human flaws.

In Jesica’s case, the cause of death was the single most common error cited in high-risk professions from aviation or medicine: the failure to share key pieces of communication.

This is what Carolyn Clancy, the new director of the Agency for Healthcare Research and Quality, which is working to reduce medical mistakes, thinks of every morning when she gets her coffee. “It occurs to me that there’s more double-checking and systematic avoidance of mistakes at Starbucks than at most health care institutions.”

The fact is that we know more about safeguards against such errors than we have enacted. Indeed, one of the difficulties of ensuring the medical equivalent of a tall/half-caf/skim latte may be in getting doctors and patients to believe there is a problem.

Last December, three years after the report by the Institute of Medicine, a survey showed that both groups still regarded medical mistakes as a relatively minor problem. If pushed, they guessed that 5,000 deaths occurred by preventable accidents, not 48,000 or 98,000. If pushed further, they were more willing to blame a person who made a mistake than the institution that might have prevented it.

Duke did something right in the dreadful aftermath of this catastrophe. Instead of hunkering down, even in the face of a certain lawsuit, they openly accepted blame and immediately adopted a new procedure. This is what’s called “Tombstone Regulations,” those sudden, piecemeal, after-the-crisis improvements.

But now, Jesica’s death at one of the country’s best hospitals is terrifyingly fresh in the minds of patients and doctors. If it happened at Duke, it can happen anywhere — and it does.

The “banality of screw-up” brings home the need for change — to create more systems that allow the open sharing of mistakes. More systems that teach the basics of teamwork.

To err, after all, is human. Human error can’t be run out of town or sued out of the profession. With Jesica on our minds, we need to be open about errors and urgent about protecting against them. We need to speak the language of safety. From A to O.