By Julie Steenhuysen

CHICAGO (Reuters) - When the SARS outbreak arrived in Toronto on Feb. 23, 2003, carried by a woman traveling from Hong Kong, the disease quickly spread to hospital workers and patients in area hospitals, ultimately infecting 257 individuals and killing 33 people.

It's a memory that hangs fresh in the mind of Dr Michael Bell, deputy director of the division of healthcare quality promotion at the Centers for Disease Control and Prevention. The Atlanta-based federal agency last week sent a team of infectious disease experts to Community Hospital in Munster, Indiana, to attend to the first confirmed U.S. case of Middle East Respiratory Syndrome or MERS.

"We take this very seriously," Bell told Reuters in an exclusive interview. "In a worst-case scenario, this could spread rapidly."

MERS is caused by a coronavirus, a family of viruses that includes Severe Acute Respiratory Syndrome or SARS, which emerged in China in 2002-2003 and killed some 800 people.

"If you recall the SARS experience in Toronto, that was something that managed to be transmitted into the healthcare facility, leading to severe illness and death," he said.

"This is not something that we want to take lightly."

State health officials in Indiana report the man is in good condition and improving daily. Hospital personnel who may have been exposed to the virus are being kept in home isolation and watched daily for the emergence of pneumonia-like symptoms. Generally the incubation period of MERS is 14 days.

The patient is a healthcare worker who on April 28 was admitted to the hospital just 30 minutes south of Chicago after having worked in healthcare in Saudi Arabia, the center of the MERS outbreak that began in 2012. So far, 262 people in 12 countries have had confirmed infections that have been reported by the World Health Organization, and another 100 MERS patients have been confirmed by other ministries of health. So far, 93 people have died.

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U.S. health officials are now checking airline manifests and contacting patients who may have been seated near the man who took a plane from Riyadh, Saudi Arabia, to London and then to Chicago, where he then took a bus to an undisclosed city in Indiana.

'ABSOLUTELY METICULOUS'

To keep the infection from spreading within the hospital, the man is being treated in an isolation room from which air is expelled through a filter, preventing it from being shared in the hallway.

"It's not because we have proof that this virus spreads easily through the air, but we don't want to take any chances," Bell said.

People who enter the room wear a respirator, a type of filtering mask that keeps them from breathing in any airborne particles in the room.

And because MERS is in a family of viruses called coronaviruses that can also be spread through contact with the patient's stool, the team is taking measures to keep all possibly infectious materials from leaving the room.

"You put on gowns and gloves before you go in the room. You take them off before you leave. You pay a lot of attention to washing your hands afterwards with alcohol gel or soap and water," Bell said.

Finally, because tear ducts in the eyes are connected to the throat, healthcare workers wear goggles or face shields to prevent any droplets from entering the eyes.

All of these measures are part of standard hospital protocols for treating various infectious diseases. People with tuberculosis are placed in airborne isolation rooms. With diarrheal diseases, healthcare workers use contact prevention measures.

"None of this is different from what the hospital is already accustomed to doing. We're just making sure the implementation in this case is absolutely meticulous," Bell said.

Bell said current hospital control measures became common practice during the HIV epidemic, when hospital workers had to assume anyone coming in the doors could be infected with the virus that causes AIDS.

"I think it's safe to say every healthcare worker, even in an outpatient setting, understands that whatever comes in the doors, they could be exposed to something infectious," Bell said.

"That ranges from something as common as seasonal influenza, or, if you work in a pediatric facility, there any number of diarrheal diseases," he said.

Despite the best efforts, however, hospitals remain a major source of infection. In March, the CDC reported that roughly one of every 25 U.S. hospital patients contracts an infection during their stay.

DISEASE POORLY UNDERSTOOD

Standard procedures for patients walking into the emergency department with a fever and respiratory complaints, as the MERS patient did in Indiana, are to put a mask on the patient and place them in room with a closed door.

"My understanding is the patient was placed in a private room very quickly," Bell said of the Indiana patient.

As for treatments, there are no specific drugs that can treat MERS, but there are basic treatments that can help the patient fight off the infection, including oxygen, which can reduce the burden on the lungs.

In addition to disease prevention experts, the CDC has sent a team of virologists to the hospital to study the MERS virus, which is still poorly understood. Although the virus first surfaced in 2012, its presence in the United States will give U.S. scientists the opportunity to study it up close.

Currently, it is not clear how the virus is transmitted, but it is clear that it can pass among individuals who have close contact with infected patients.

"The good news is that it's a group of viruses that have a very delicate envelope or membrane on the outside. Because of that, the virus tends to be rapidly inactivated by disinfectants," Bell said.

Since March of 2014, there has been a spike in the number of cases reported in Saudi Arabia. Bell said it is not clear whether that represents a change in the virus that makes it easier to spread, or an increase in the number of cases being reported to health officials.

"That is completely unknown at the moment. It's still rather early in terms of the viral characterization. Since this has all been happening outside the U.S., it's not something we've had a lot of time to work on."

At this point, the CDC has not issued any restrictions on air travel, but Bell said the case makes clear just how easily infections can spread. He recommends that people traveling through airports try to limit what they touch, and wash their hands frequently.

(Editing by Eric Walsh)