Still, the infection seems to have been contained. No one has gotten sick since Thursday, said Dr. Dean Sienko, director of the Ingham County Health Department.
Late Tuesday afternoon, the East Lansing school e-mailed students, advising them to seek treatment and contact the health department if they'd been sick in the past week with "gastrointestinal symptoms ... especially bloody diarrhea."
Just hours earlier, the health department was notified that lab tests had confirmed the strain as E. coli 0157:H7.
The infected MSU students may represent a fraction of those infected, Sienko said.
"Typically, what you see is the tip of the iceberg. There are more people who don't get that sick or don't seek medical attention for whatever reason," he said. "Those people are under our radar screen."
Additional information may help investigators pinpoint the outbreak's source, but that could take days because it requires meticulous interviewing of the students, several of whom remain hospitalized, Sienko said.
"I look at these things two ways -- is there an ongoing public health threat? I have no evidence this is the case. Now, we have to determine what went wrong," Sienko said.
Both he and the university's chief physician, Beth Alexander, cautioned against rushing to judgment. The infected students all lived on campus, "but people don't always eat on campus," Alexander said.
Students are going about their daily business, said Chris Kulesza, 20, of Troy, chairman of MSU's Academic Assembly.
Many just learned about the outbreak Monday or Tuesday, and most feel the scare by then was contained, he said.
The Centers for Disease Control and Prevention estimate this strain of E. coli infects 70,000 people a year, killing about 60, mostly young children and elderly people. It comes from a variety of sources such as undercooked meat and vegetables that have been watered by a contaminated source.
In 1993, investigators linked an E. coli 0157:H7 outbreak that resulted in four deaths and hundreds of infections to tainted meat at Jack in the Box restaurants.