Hundreds of scientists are working around the clock to find out more about a mysterious microscopic killer that has already claimed at least 81 lives worldwide.

The scientists work in a network of 11 labs in nine countries to try to find out as much as possible about the cause, onset and transmission of severe acute respiratory syndrome, known as SARS.

More than 2,200 people have been diagnosed with the disease, with at least 115 cases suspected in the United States.

Laboratories in the research network, created by the World Health Organization, are classified as P-3, the second-highest hazard containment level, and workers observe strict protocols for everything from transporting blood and tissue samples to testing nasal swabs.

``It has been handled very well so far,'' says Dr. W. Grant Starrett, an infectious disease specialist at Good Samaritan Hospital in Dayton.

``The fact that there are no deaths here in the United States speaks to that. Public health is a science that has matured, and we are reaping the benefits of that,'' he said.

So far, it appears that the death rate is lower for SARS than for epidemic influenza, according to the Centers for Disease Control and Prevention in Atlanta. In other words, most of those who contract SARS seem to recover.

But scientists are just beginning to understand the disease. These are things we know about who is at risk and what can be done to treat and stop SARS:

Q. What are the symptoms of SARS and how do doctors diagnose it?

A. There is no test available for SARS, though researchers are working to develop one. To diagnose SARS, physicians use a ``case definition'' of the disease, checking to see whether certain symptoms and conditions are present. To be diagnosed with SARS, a person must have:

-- A temperature greater than 100.5 degrees, and;

-- Symptoms of respiratory illness such as coughing, shortness of breath, difficulty breathing or hypoxia; or X-ray evidence of pneumonia or acute respiratory distress syndrome; and

-- Traveled within the last 10 days to China, Hong Kong, Vietnam or Singapore; or

-- Come in close contact in the last 10 days with someone who has traveled to one of those areas, who has been diagnosed with SARS or who has been in close contact with a SARS patient.

Q. How is SARS transmitted?

A. Authorities believe the most common method of transmission is through the droplets formed when an infected person coughs or sneezes. But they also are investigating possible transmission of the virus through contaminated objects. As with other viruses, not everyone who comes into contact with the virus develops the illness.

Q. How long does it take for the disease to develop?

A. The incubation period for the disease is two to 10 days. Researchers have developed two diagnostic tests for a coronavirus thought to be responsible for causing SARS, but they must still test a large number of people to determine if the tests are accurate.

Q. What is the treatment for SARS?

A. Patients in the United States are being treated as if they had pneumonia, and antibiotics are prescribed if it seems necessary. There is no proof that any anti-viral therapy or steroid treatment targets this coronavirus, though those have been tried.

Q. What should I do if I have all the symptoms of SARS?

A. If you have the symptoms and have traveled to Asia within the last 10 days, call your family physician, Starrett said. Your doctor will give you further instructions. Try to cover your mouth and nose when you sneeze, and wear a mask if possible. Wash your hands often and thoroughly, especially after blowing your nose. Do not share silverware, towels or bedding with family members until those items have been washed in soap and hot water. Keep surfaces such as counters, door knobs and bathroom fixtures clean by using household disinfectants and disposable gloves.

Q. What else is known about this coronavirus?

A. Coronaviruses are a family of viruses that have a halo of spikes when viewed under a microscope. These viruses are a common cause of respiratory illnesses in humans. The cold virus, for example, is a coronavirus. Scientists think the particular coronavirus causing SARS is either a virus that normally infects humans but which has recently mutated to become more deadly, or is a virus that normally affects animals and is now attacking humans, Starrett said.

Q. How close do you have to be to a SARS patient to contract the disease?

A. This is something that health authorities are still trying to determine. The official definition of close contact is ``having cared for, having lived with or having direct contact with respiratory secretions and/or body fluids of a patient known to be a suspect SARS case.''

Q. What sorts of precautions are U.S. hospitals taking to prevent the spread of SARS?

A. When a person suspected of having SARS is admitted to a hospital, he or she is placed in isolation. Anyone entering this patient's room wears a disposable gown and washes his or her hands. Health care workers also wear masks when near the patient, and the patient is placed in a room that is specially ventilated. This way, Starrett says, ``the rest of the hospital is not exposed to whatever that person might be coughing up.''

Q. Should I cancel travel plans?

A. The CDC issues travel guidelines on its Web site, www.cdc.gov. It strongly advises people not to travel to China, Hong Kong, Singapore and Vietnam unless it is absolutely necessary.

Sources: Dr. W. Grant Starrett, infectious disease specialist at Good Samaritan Hospital in Dayton and clinical assistant professor of medicine at Wright State University; the Centers for Disease Control and Prevention (www.cdc.gov); and the World Health Organization (www.who.int/en/)