Two years ago, health officials were alerted to a nationwide outbreak of deadly Salmonella Typhimurium.  Eventually, the source was traced by epidemiologists at the Minnesota Department of Health.  Here’s how they did it.

In 2008, 78-year-old Clifford Tousigant reluctantly moved into an assisted care facility in Brainerd, Minnesota.  A Korean War veteran with three Purple Hearts, he valued his independence.  But he soon adapted to his new life, puttering around the grounds in his motorized chair, entertaining his grandchildren, watching Vikings football games and enjoying his nightly peanut butter sandwich.

Until Dec. 28, 2008, when he came down with painful stomach cramps and diarrhea.  Two days later he was rushed to the hospital.

Minnesota Health authorities quickly analyzed his stool sample, and confirmed what they feared: Tousignant had been sickened with Salmonella Typhimurium, and the strain matched the genetic fingerprint of sick people across the nation.

For weeks, epidemiologists in states from California to Connecticut and at the Centers for Disease Control and Prevention (CDC) had monitored the outbreak, interviewing scores of victims.  But the epidemic would continue until somebody tracked the disease to its source, and the experts were baffled.

It would take the Minnesota Health Department (MDH) two weeks to solve the deadly puzzle, demonstrating why that small cadre of epidemiologists in St. Paul is widely considered the best in the business.

Dr. Kirk Smith, a softspoken scientist who grew up on a North Dakota farm, heads the foodborne illness unit, which operates out of a modern, steel and glass office building near the state capital.  Like other epidemiologists, Smith had learned his craft dealing with smaller outbreaks of food poisoning, typically traced to a single restaurant, a church potluck or a cruise liner’s kitchen.  But the pattern of food poisonings had been changing over the previous decade or more, and epidemiologists were struggling to keep up.

Based on the data from PulseNet, the nationwide database at the CDC, more than 110 people in at least 17 states had been sickened from the same source.   They included a 72-year-old woman in northwest Minnesota who had died on Dec. 21.  The following day, the staff of the Brainerd nursing home called MDH to report they had three more Salmonella cases in their institution.

“That’s when we got cracking,” Smith recalls.  “But we had scant epi information from those other states, no thorough food histories.  Local health departments typically do cursory interviews.  Did people eat at a local restaurant? Spent time at a daycare center?  Had contact with poultry or a reptile?  Those investigations work for small, local outbreaks, but not for these regional and national cases.”

At MDH, a carefully trained team of student workers popularly known as “Team Diarrhea” was already at work, interviewing victims and nursing home staff.  What had people eaten in the last week?  Where did they eat it?

“By the time we hear about a case, it’s typically at least two weeks old,” Smith explains.  “There’s the incubation period.  And people generally wait a few days before they see a doctor.  And then the doctor may not take stool samples right away.”

So Team Diarrhea was asking sick people what they ate two or three weeks earlier. By Jan. 1, Minnesota had multiple cases traceable to the same outbreak, but still no clue to the source.

Then they thought they got a break.  Several sick people had eaten at the same restaurant in Ohio, and some of them matched the national outbreak strain.

“We thought we had something,” Smith recalls.  “But it was a coincidence.  They just happened to eat at the same place where there was a smaller outbreak, but that restaurant had nothing to do with the national outbreak.   We were back to Square One.”

Meanwhile, the epidemic raged on, with new cases being reported daily.  On Jan. 4, a resident of another Brainerd home died.   Cliff Tousignant remained hospitalized, exhausted by recurring bouts of diarrhea, stomach cramps and blood draws.  His sons and grandchildren took turns at his bedside, catching him up on family news.

Back at MDH, scientists groped for something suggesting a pattern.  In other states, investigators were focusing on chicken, but the Minnesota investigators began to see another possible culprit.  Some of their victims had eaten chicken, but others had not.  But eight sick Minnesotans all had eaten peanut butter.

“Then we got another case in another nursing home in the northern part of the state, and it turned out to be the same outbreak strain,” Smith recalls. “And we had sick kids in an elementary school, also in the north.  So we had sick people in three institutions, all in northern Minnesota.”

Carlota Medus and Stephanie Meyer, both veteran epidemiologists at MDH, pursued that thread.  Something at three north state institutions was making people sick, and it had to be something that was not served at institutions in the southern part of the state.  But what?

They obtained copies of invoices of food purchases at each of the nursing homes and the school, stacked them on a table and went to work.  The process isn’t sexy, nor technical; it’s more gumshoe drudgery.  But, for health investigators, institutional outbreaks offer an advantage: Since food is purchased in bulk, authorities can track food back to the distributors.  If people are being sickened at one institution but not at another, the invoices may hold a clue.

Medus read her invoices aloud, and Meyer checked to see whether that product was listed at the other institution.  Frozen chicken?  How about spinach? You got green beans?  What brand?  Canned or frozen?

What about peanut butter?  All three northern institutions had bought peanut butter from a Fargo distributor, while institutions in the south got a different brand from a different distributor.  The Brainerd people got sick.  The south state people did not.  Bingo, they had a suspect.

The difference was a five-pound, institutional tub of King Nut Peanut Butter.  Minnesota Agriculture authorities obtained the jar and tested it for Salmonella.  The results were positive.

“That was crucial,” Smith recalls. “But the jug was open, which means it could have been contaminated after opening.  And it doesn’t explain all those other, non-institutional cases.”

Still, he and other state authorities decided that the evidence, while not conclusive, was strong enough to issue a public warning not to eat King Nut peanut butter.

From there, events began to cascade.  King Nut recalled its peanut butter, while federal authorities converged on a Georgia plant that manufactured the raw peanut paste used to make King Nut and thousands of other products.

On Jan. 16, Connecticut officials located an unopened jar of King Nut, and it tested positive for Salmonella.  The Peanut Corporation of America announced a nationwide recall of products made from their peanut paste — hundreds of brands of crackers, cookies, snack bars, even pet snacks.

It was too late for Tousignant.  On Jan. 12, he died of food poisoning.

In the end, the PCA outbreak was blamed for 714 illnesses and nine deaths in 46 states.  The CDC estimates that for every Salmonella case that is diagnosed, about 40 other cases are not identified, suggesting that some 28,000 people may have been sickened.

ut Minnesota’s dogged detective work, coming at the height of a national epidemic, certainly halted the spread and prevented thousands more illnesses and possible deaths.