By late last week, there were more than 4,800 cases of SARS in 27 countries and 293 deaths - small numbers in the scheme of global threats. Many people couldn’t help but wonder if health officials and the media were manufacturing hysteria over a microscopic bug, now that Iraq was no longer fodder for 24-hour cable news. But the insidious nature of the virus, its capacity to spread and kill, remained. And its lingering mysteries - how it’s transmitted, why it’s more virulent in some people than others, how it’s best treated - have public-health experts discernibly worried and unapologetic for erring on the side of caution. In the United States, where the tally ( 记录 ) of “suspect” and “probable” cases is fewer than 300, with no deaths, there was still concern: Could the epidemic spread further? Why hasn’t it? How worried should we be? The medical battle is being fought on multiple fronts: doctors are trying to diagnose, treat and contain the virus. Scientists are launching seek-and-destroy missions in petri dishes ( 有盖培养皿;营养皿 ). And public-health officials are mapping strategies for drug and vaccine development. As with any new enemy, victory will not come easily - or quickly. “This is still a work in progress,” said Centers for Disease Control and Prevention director Julie Gerberding last week. “We have a lot to learn.” The fear is that we don’t know exactly how the virus speads. While it’s clear that it jumps from person to person through airborne droplets - a sneeze or a cough - experts suspect it may be transmitted fecally as well. In Hong Kong, residents who contracted SARS in a housing complex, Amoy Gardens, suffered severe diarrhea, and experts found coronavirus in feces and on an infected resident’s toilet. Health officials concluded that the pathogen spread at least in part through breaks in the building’s sewer lines. Worldwide, experts are also working hard to determine how long the SARS virus survives in the environment - on countertops or door handles - and whether that might contribute to its spread. Treatment is another puzzle. The illness is caused by a virus, rather than a bacterium, so antibiotics are ineffective. Hong Kong doctors are using the antiviral drug Ribavirin, often in combination with steroids, but U.S. researchers say the drug has no effect on the SARS virus in a lab. At the United States Army Research Institute for Infectious Diseases in Frederick, Md., scientists are conducting a treasure hunt for treatment. Every few days, a shipment of drugs collected from the National Institutes of Health and drug manufacturers around the world is delivered to a team of virologists led by John Huggins and Peter Jahrling. With every step forward, new mysteries arise. Last week a Canadian virologist, Dr. Frank Plummer, questioned the link between the coronavirus and SARS altogether, announcing that he’d found evidence of the virus in only 40 percent of patients. The data are troubling, but other scientists say a number of factors could account for the finding, including weak or incomplete diagnostic tests. Halfway around the world in Hong Kong, doctors were reporting patients who tested postitive for SARS - but had none of the classic symptoms. And then there’s Sam Sun, a third-year law student in Beijing, who was cooped up in his dorm rrom after classes were canceled last week. “I’m worried,” he said. “I don’t know when this will end.” The fact is, SARS may never be vanquished, but its lessons are preparing scientists for whatever comes next.