Pam Steele was 38 and eight months pregnant in 1990 when she battled what she thought was a severe case of flu. The diagnosis: listeriosis, caused by the microorganism Listeria monocytogenes. Steele’s daughter was stillborn, and Steele nearly lost her own life.

“I had had problems getting pregnant, but everything seemed to be going OK,” said Steele, of Cambridge. “It was devastating. I couldn’t help but wonder, where did I get this? That’s the scary part. We never figured it out.”

Now, Steele is helping researchers solve such mysteries.

Lydia Medeiros and Jeff LeJeune, food safety scientists with the Ohio Agricultural Research and Development Center, have teamed up with Colorado researchers in a $600,000 study to examine how Listeria might enter people’s homes and kitchens.

Only about 1,500 to 2,500 Americans get listeriosis each year, but a significant number — 500 — die. In Ohio, the Department of Health officially reports 37 cases annually, with the probable actual number twice as high. It’s estimated listeriosis costs Ohioans $74 million each year.

Its high mortality rate has always made listeriosis a serious concern. But the disease made headlines in 1998 when 40 people in 10 states became ill and four died due to undercooked hot dogs.

Despite similar periodic outbreaks, most cases occur erratically, Medeiros said: “We just don’t know where sporadic cases come from.”

During their study’s first six months, the researchers signed up 27 of 50 households they want to examine. Half of the families live on dairy farms or around five or more cows, sheep, or other ruminant animals, which tend to shed Listeria in their feces.

“We are partly looking at this as an occupational safety and health issue,” LeJeune said. “Are farm families more exposed to Listeria monocytogenes? Are farmers bringing their work home with them — literally — on their clothing? If that is occurring, how can we interrupt the pattern?” Nonfarm rural households act as controls. The researchers use molecular biology to conduct DNA sequence analysis of any Listeria bacteria they find to help determine if Listeria found in different places comes from the same source.

Medeiros said patterns are emerging. “We’re discovering what the most important factors in controlling listeria are,” she said. “Next year, we’ll teach participants how to control factors that put them at risk, and in the third year we’ll go back and reassess. There has never been a study to do this.”

Now 54, Steele has a 10-year-old son — the result of a pregnancy many thought wasn’t possible after her bout with listeriosis. She is proud to participate. “When I saw the notice in the newspaper, I knew immediately I would sign up. What’s important is finding information that can help someone else.”