BOSTON -- She hits the halls like a cop on the beat.

“When I first arrive on a unit I do what I call a drive-by.”

Part of her job is to go undercover at Massachusetts General Hospital to make sure doctors, nurses and health care workers are washing their hands both as they enter and leave patient rooms.

“We're not being sneaky about it in any way,” said the longtime nurse NewsCenter 5 agreed not to identify. “Hand hygiene is really the single most important thing that anyone can do to stop of the transmission of germs that can cause infections.”

‘As simple as it seems, hand washing is a really challenging problem,” said Dr. Ravin Davidoff, the chief medical officer at Boston Medical Center.

As recently as five years ago, officials at even some of the world’s most respected hospitals admitted that they could only get employees to wash their hands about half the time. Compliance rates averaged between 40 and 50 percent. It was a big problem. In 2003, the Centers for Disease Control and Prevention estimated there were 2 million hospital-acquired infections in the United States, leading to 90,000 deaths.

Local hospitals were no different.

“No, we were average like everyone else,” said the Massachusetts General Hospital employee now charged with policing hand hygiene compliance.

In response, hospitals have gone on the offensive, launching a variety of programs to enforce best practices. Everyone from the top attending physicians to food service workers and housekeeping attendants – anyone who comes into contact with hospital patients – must use hand sanitizer or soap and water as they enter and exit a room.

Massachusetts General Hospital deploys so-called secret shoppers, or “Cal Stat cops,” named after the commonly used alcohol-based hand sanitizer. They patrol the various hospital departments, watching for compliance, then gather statistics and report back to each department.

Beth Israel Deaconess Medical Center posts compliance rates online.

Tufts Medical Center posts colorful posters in nearly every hallway and patient room to drive home the point.

Boston Medical Center uses clever buttons that ask, “Got hands? Wash them.” The hospital also uses bacteria cultures to make the point. Bacteria from an employee’s hand is sent to the lab and cultured both before and after they wash.

“It really gets people to notice and say, ‘I know what you're talking about now,’” said Davidoff.

All the creative approaches have a deadly serious goal, which at most Boston hospitals, is getting seriously good results.

MGH just threw a cake party for employees after achieving 90 percent hand hygiene compliance hospital-wide for three months in a row.

“We've seen over a two-and-a-half-fold decrease in the hospital-acquired cases of MRSA” since new the hand hygiene protocol went into effect, said Dr. David Hooper, chief of infection control at MGH.

Tufts Medical Center’s and Boston Medical Center’s most recent compliance rates are also over 90 percent.

“Our infection rates have come down dramatically over the past few years,” said Davidoff. “Part of that, we believe, relates to our hand washing efforts.”

Reminders and dispensers seem to be everywhere at hospitals. Infection control experts said convenience is critical to encourage hospital workers to make hand hygiene a part of their work flow.

They also encourage every worker to speak up if they see a colleague forget to wash their hands, a challenge in the hierarchy of hospitals.

“We have gone out and encouraged nurses, and any health care worker, to say to an attending physician, 'excuse me you forgot to wash your hands,'” said Davidoff.

Hospitals also encourage patients to speak up if they notice a health care worker forget to wash. In addition to saving lives, not having to treat all those infections saves the health care system countless dollars.