An outbreak of salmonella food poisoning infected about 140 people at Northeastern University in the past three weeks, causing university officials to close two cafeterias.

The Northeastern health center confirmed over 100 cases of the infection among students and another 30 among cafeteria workers. The illness, discovered during freshman orientation week, sent 11 students to the infirmary for several days to recover from severe dehydration, diarrhea, and vomiting, Dr. Job E. Fuchs, director of the health center, said yesterday.

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The recent food poisoning "is the largest outbreak of salmonella I've seen," Fuchs said, adding that "some cases were mild but some were just miserable."

Health center officials closed the cafeterias after 25 cases of the infection were reported. The cafeterias have since reopened.

The health center believes that cafeteria workers carried the salmonella bacteria into two dining halls, Fuchs said, adding that 30 workers had positive stool test results.

"It's hard to explain how so many employees could have been infected. They probably shared a common meal," he said.

The Boston City Hospital is still investigating the source of the poisoning. Dr. Cynthia Trumpp, an epidemiologist at the hospital, said yesterday, adding that doctors have discovered a batch of infected chicken salad but have not yet concluded that it is the source of the poisoning.