Dr. Ruth Lynfield knows the numbers sound terrifying: 30,000 dead. 170,000 hospitalized. More than a million people infected -- all in Minnesota alone. But she doesn't want people to get the wrong idea. As state epidemiologist, it's her job to lay out all the possibilities for the next wave of swine flu, including the worst-case scenario. Now, with summer winding down and students returning to school, she's out to make sure that Minnesota avoids the worst case and gets safely through the first worldwide flu pandemic in 40 years. It's a challenge the transplanted New Yorker and pediatrician has handled gracefully since the virus surfaced in April. "She knows so much and she's so smart," said Dr. Sanne Magnan, the state health commissioner. "She's very good at grounding us," Magnan said. "We're lucky to have her." At public appearances, Lynfield, 48, has become known for her calm recitation of the facts, laced with a subliminal message rooted in her natural optimism: "It will be challenging, but we'll make it through." For months, Lynfield has been tracking the swine flu outbreak in Minnesota and refining contingency plans. She's helping to lead a small army of about 200 staffers at the Minnesota Department of Health who have been deployed to the flu watch.

In endless meetings, they chew over the details of one possibility after another. What if a plane arrives in Rochester and a passenger is infected with a particularly deadly strain? How would they notify the other passengers?

What about the infected person -- could the state force him to stay home? "If they're quarantined, yes," Lynfield tells colleagues at one planning session. "That's the point of quarantine."

What if the patient doesn't cooperate? Well, she replies, they could post a police car outside his home. "They ended up doing this in one or two cases in Toronto" during the SARS outbreak, Lynfield adds. "But we're optimistic it won't come to that."

The questions don't stop even during her free time. Lynfield can be weeding the garden or attending a child's sporting event, and someone will approach her to talk about the flu. "Sometimes they're looking for reassurance," she said. Sometimes they want to vent.

"There are some people who feel like we in the public health world may have overblown the situation," she said. "And then there are other people who are very concerned, very worried."

Her message to both is pretty much the same. No one knows what's coming, "so the prudent thing to do is plan as best you can."

In a sense, Lynfield has been preparing for this moment for much of her career.

The daughter of two physicians, she trained as a specialist in children's infectious diseases and taught for five years at Harvard Medical School. But she gave up treating patients to work in public health, fighting outbreaks. "I feel, at least for me, you can make an impact on a larger scale," she explained.

Handling of pork-plant case wins admiration

Since moving to Minnesota in 1997 with her husband, Dr. Mike Sethna, and three children, Lynfield has spent a dozen years at the state Health Department, trying to detect and prevent outbreaks of food poisoning, tick-borne illnesses and contagious diseases, from hepatitis to HIV.

Petite and energetic, Lynfield bears down on problems with a scientist's intensity. "She does get excited when she's on the brink of understanding something," said Magnan. "You can see the eyes twinkle."

One of her biggest cases turned up in 2007, shortly after she was named state epidemiologist. Eleven workers at Quality Pork Processors, a plant in Austin, developed a strange nerve disorder. Lynfield led the state investigation that helped solve the mystery.

"We admire her enormously," said Carole Bower, the plant's nurse. At the time, she said, plant officials were worried about panicking both customers and employees. But Lynfield helped allay fears, she said, when she spoke publicly about the investigation, carefully explaining what they knew and what they didn't know. "She's very professional," Bower said, "very sensitive to public concerns."

Eventually, investigators traced the problem to a device used to process pig brains. The plant shut down the process and hasn't had a new case since, Bower said.

Experts have been saying for years that another global flu outbreak was inevitable; a novel flu strain sweeps the globe roughly every 30 or 40 years. The last one, which was relatively mild, came in 1968. The next one, they feared, could kill a significant proportion of its victims, like the 1918 Spanish flu.

Pinning hopes on vaccine

In April, it looked like the worst case might have arrived.

Lynfield, like her counterparts all across the country, went on alert after news reports that young people were dying of a new flu in Mexico, and that a few cases had crossed the U.S. border.

But by early May, as cases popped up across Minnesota, it was obvious that this was not a particularly fearsome virus. Although highly contagious, its fatality rate was about the same as seasonal flu.

Still, influenza is a "quick-change artist," as Magnan points out. Experts warn that it could infect between a third and half the population, and depending on severity, send hundreds of thousands to hospitals and intensive care units.

Since spring, Lynfield has spent 12-hour days trying to study the outbreak, learn from it and tweak plans for the fall.

Now they know some things they didn't in the spring: It hits children, pregnant women, obese people and people with asthma hardest of all.

Even if it doesn't get worse, Lynfield said, the next wave of swine flu will be pretty disruptive, with soaring absentee rates and a rush on hospitals and clinics. If the virus mutates, things could get much more dramatic: By one estimate, more than 30,000 could die in Minnesota alone, if it mimics the 1918 pandemic.

Michael Osterholm, a former state epidemiologist (and Lynfield's onetime boss), said there's no point in downplaying the potential danger. "What you have to do is give all possibilities," he said. "If that scares people, that's unfortunate. ... What we want them to do is actually be very concerned."

Still, Lynfield is pinning her hopes on a vaccine, which is expected to start arriving in October. She hopes that, and all the obsessive planning, will minimize the damage.

"In public health, if we're successful, people don't know that something happened," she said. "The best thing that will happen is people will come back and say, 'Eh, what was all the hype about?' That means we were successful."

Maura Lerner • 612-673-7384