CHICAGO—Two months ago, staff at Chicago's Mercy Hospital and Medical Center participated in an active shooter drill.
That training came into play and likely saved lives Monday when a gunman opened fire on the hospital campus. The tragedy left four people dead: a physician, pharmacy resident and police officer as well as the gunman.
The incident began Monday afternoon in the hospital's parking lot when the suspect, identified by police as 32-year-old Juan Lopez, shot his former fiancee, Dr. Tamara O'Neal, an emergency department physician during a domestic dispute.
Police arrived on the scene and exchanged gunfire with the suspect before he ran into the hospital and fatally shot Samuel Jimenez, a 28-year-old Chicago police officer, and Dayna Less, 25, a pharmacy resident.

Chicago police work the scene after a gunman opened fire at Mercy Hospital and Medical Center Monday. (Associated Press)
The emergency department reopened Tuesday afternoon and the hospital was nearly fully operational with the exception of a few outpatient clinics that remained closed, Dr. Michael Davenport, Mercy's chief medical officer, said during a news conference Tuesday.
Davenport credited the active shooter training for minimizing the loss of life and injuries, which he said was prompted by the rash of mass shootings seen across the country in recent years.
"The active shooter drills were prompted by the changes and the activities in the world we live in," Davenport said. "All of us have been affected—though you would like to think a hospital is a safe place, we know that schools are no longer safe, so we thought it was prudent that we begin to teach our people to be prepared."
The training included online education for all employees and training with simulations for hospital leaders, which was followed by an active shooter drill.
"It absolutely helps," Davenport said.

Dr. Michael Davenport (center), chief medical officer at Mercy Hospital and Medical Center, speaks to reporters Tuesday a day after a shooting incident left four people dead, including the gunman. (Steven Ross Johnson)
The increased frequency in which mass shootings have occurred in public places over the past decade has made training for such incidents an integral part of disaster preparedness training for school employees and government workers.
Traditionally, hospitals have prepared for such incidents by undergoing triage drills and ensuring enough resources are on hand to receive a sudden influx of victims.
Hospitals are required by the CMS to develop an emergency plan to respond to "every emergency in a timely, collaborative, organized, and effective manner," according to the agency's website. An emergency plan includes having risk-assessment policies and a communications plan, and then routinely training and testing the plan's effectiveness.
While the CMS focuses its resources primarily on preparing healthcare providers for such disasters as a flood, fire or flu pandemic, an increasing number of hospitals like Mercy in recent years have voluntarily taken steps to prepare for the possibility of a shooting within their own facilities.
"We see more hospitals more interested in this type of hazard," said Kyle McPhee, director of preparedness for Hagerty Consulting, which works with hospitals and health systems top develop emergency preparedness plans for active shooter events.
Erik Modrzynski, a former firefighter and the current emergency manager at Medical University of South Carolina, Charleston, said back in June the majority of active shooter training that was done at the facility when he first arrived three years ago was classroom presentations. He decided more hands-on training was needed. He got certification from the Alert, Lockdown, Inform, Counter, Evacuate Training Institute—known as ALICE—to develop a training program that was more scenario-based.
"It's live action the way we do our training," Modrzynski said. MUSC coordinates with local law enforcement to conduct a live drill once a year, with police arriving on the designated day posing as shooters and requiring employees to apply the lessons they have learned through training.
A similar type of training was conducted last November at Elmhurst (Ill.) Hospital in suburban Chicago. In addition to classes that teach staff to either "evade, hide or fight" during an active shooter event, the provider also engaged in a full-scale, mock shooter scenario.
"This all happens within seconds to minutes," said Karen Forte, system manager for emergency preparedness at Edward-Elmhurst Health.
Such cases require healthcare professionals to make difficult decisions, including addressing their own safety before ensuring the safety of their patients, which Forte acknowledged was a rule many clinicians found difficult to follow.
"Most nurses and doctors are aghast about leaving patients behind," Forte said. "It's definitely a challenge."
But protecting patients is a factor that can't simply be overlooked, said Eric Chetwynd, general manager of healthcare solutions at emergency consulting firm Everbridge.
As in the case of Mercy, Chetwynd said a typical shooter will enter a hospital through the emergency department because it is the most accessible. He said a typical response plan would be to lock down the ED and isolate it from the rest of the hospital to restrict the movement of the assailants while protecting admitted patients.
Having a rapid response communications system in place was essential for fast-moving emergencies such as a shooting event, Chetwynd said. But ultimately, an effective response comes down to how well-drilled the staff is to face such emergencies.
"You certainly don't want the moment of an active shooter coming through the door to be the first time everybody tries to figure out how to use their systems and what the plan is," Chetwynd said.