Esther Mok has had a truly horrible two months. The 26-year-old former flight attendant from Singapore came down with SARS and survived. But she infected both of her parents and her pastor, all three of whom died. Then she faced the wrath of her nation. ''Esther Mok infected the whole lot of us,'' seethed Singapore's health minister Lim Hng Kiang at an early April press conference in which he addressed the hundred or so cases of SARS in that country.

Through no obvious fault of her own, Esther Mok had been branded a ''superspreader''- a hellcat who threatened, almost literally, the entire planet. That word doesn't appear in many medical dictionaries yet, but authorities from Fox News to the World Health Organization have invoked it to explain SARS's rapid sweep across the world. On April 5, Dr. Robert Breiman, a WHO team leader in China, said he was especially interested in ''the phenomenon of `super spreaders'-people who seem to spread their disease to a lot of other people.''

But are superspreaders really to blame? Now that the SARS epidemic may be slowing, one thing is clear: The more we know about how SARS works, the less it seems the world was ever really threatened by poor Esther Mok in the first place.

Though the term ''superspreader'' is new, the idea that particular individuals have an outsized role in fueling epidemics isn't. In early 20th-century New York, before health inspectors finally got wise, a cook named Mary Mallon infected with typhoid seven different families that employed her. ''Typhoid Mary'' felt fine and didn't understand why the inspectors wanted to test her blood and stool, so she assaulted them with kitchen implements and fled. Eventually captured and banished to New York's North Brother Island, Mallon won clemency after three years of isolation-only to cause another outbreak after returning to work as a cook under a pseudonym.

The most famous contemporary superspreader is Gaetan Dugas, the French-Canadian flight attendant who had sex with thousands of men all over the world in the late 1970s and early `80s. Immortalized in Randy Shilts's 1987 book ''And the Band Played On,'' Dugas was no doubt responsible for a large percentage of early AIDS cases, though just how many remains in dispute. Like Mary Mallon, Dugas hardly cuts a sympathetic figure. According to Shilts, Dugas would sometimes turn on the lights in a bathhouse after an anonymous encounter, revealing the purple lesions on his body to his partner. ''Gay cancer,'' he would say. ''I'm going to die and so are you.''

The idea of pinning the blame for an epidemic on a single individual has great psychological and media appeal. Scapegoats comfort mass hysteria even as they fuel it. But of course, the superspreader concept also has great potential value in stopping the spread of disease. If a few people do in fact bear direct responsibility for the way a disease spreads-whether because of their behavior or the particular strain of the disease they carry-identifying and containing them could knock the disease out in the first round.

But determining whether or not superspreaders fuel an epidemic is a tricky business. For one thing, it's necessary to understand how a disease is actually communicated. Although medical researchers have identified the coronavirus that likely causes SARS, the actual mechanics of transmission remain something of a mystery. SARS is probably spread through coughing, but it also might have spread at least once through contaminated fecal matter passing out of a faulty sewage system.

Even if we assume that SARS spreads mainly through human-to-human contact, individual superspreaders may not deserve nearly as much blame as the term implies. It depends in part on how infected people are connected to each other.

Recently, scientists and sociologists have called attention to what they call ''scale-free networks.'' As the Notre Dame physicist Albert-Lszl Barabsi argues in his popular 2002 book ''Linked: The New Science of Networks,'' understanding such networks can explain everything from how certain diseases travel to why Kevin Bacon can be linked, in the pop-culture parlor game, to most other Hollywood actors in four steps or less.

In contrast to scale-free networks, bell curves, or what statisticians tellingly call ''normal distributions,'' describe most of the statistical phenomena in our lives. There's an average, and there's some spread around that average. Most adults are between five and six feet tall. A couple guys on the Celtics are a little taller than that; some of the people you see on the T may be a bit shorter.

Scale-free distributions have an average, too, but they also include points that are spread wildly far apart. If height were scale-free, most humans would still stand between five and six feet, but some would grow to be 100 feet tall. In a population of 6 billion, there would be at least one man standing at sea level who could comfortably gaze over the 6300-foot summit of Mount Washington.

Though some epidemiologists dispute the data, there's good evidence that the number of our sexual partners is distributed in a scale-free way. ''Most individuals have very small numbers of sexual partners, but there are a few with outrageous numbers,'' says Lus Nunes Amaral, a professor of chemical engineering at Northwestern University who has studied the topic. The average American will have about a half-dozen sexual partners in his or her lifetime. A Wilt Chamberlain or a Gaetan Dugas will have thousands.

According to Barabsi, these individuals aren't just interesting because they're atypical, but because they serve as network hubs connecting everyone to everyone else, in a few short hops. ''When it comes to viruses and epidemics, hubs make a deadly difference,'' he writes in ''Linked.''

But health officials are beginning to suspect that SARS patients are not, in fact, connected this way. Despite its initial interest in the theory, the World Health Organization has begun attempting to temper speculation that superspreaders play a major role in transmitting the disease. The spread of SARS ''probably follows a normal distribution,'' says Megan Murray, a professor of epidemiology at the Harvard School of Public Health. While especially mobile people, like flight attendants, may indeed spread the disease more quickly than others, the SARS epidemic may be no more marked by superspreaders than the spread of the common cold is.

International health officials do think that some people with SARS are slightly more contagious than others. But when it comes to estimating how many people one individual patient has infected, the most important factor is whether that individual caught the disease before the public-health system knew how to respond. According to WHO's April 15 advisory on superspreaders, ''Since infection control measures have been put in place, the number of new cases of SARS arising from a single SARS source case has been significantly reduced.'' And if a so-called superspreader is just someone who coughs a lot and spreads a disease before we know what's going on, the concept doesn't really help us in stopping the next outbreak.

The man who is probably responsible for the most SARS infections is a Hong Kong airport worker who may have infected as many as 112 people. But he didn't infect them because of any particular behavior on his part, or because of some particular strain of the disease that he carries. He infected them because his doctors, having little understanding of the disease, placed him on a jet nebulizer that sprayed medicated mist into his lungs. Every time the man exhaled, he infected people around him. He didn't spread SARS to individuals particularly likely to spread it again, and there's nothing about his case that suggests that he'll spread SARS to a particularly large number of people in the future, either.

Since the word ''superspreader'' doesn't have a precise, universally accepted definition, we can't say with certainty whether the man with the nebulizer is one. What's clear is that he's not a network hub.

Dr. Kent Sepkowitz, the director of infection control at the Memorial Sloan-Kettering Cancer Center, notes that people who cough a lot around other people have always spread illnesses-and that there's nothing atypical about them that would merit tagging them as superspreaders.

''I don't think there's anything going on beyond the basic principles of transmission,'' he says.