An unusually large outbreak of food-borne illness is making scores of Boston College students sick and has been linked to an intestinal germ that disease trackers suspect spread through fare served at a Chipotle Mexican Grill in Cleveland Circle.
Laboratory tests on five samples from infected people confirmed what health officials had suspected based on the symptoms: that the culprit is norovirus, and that the illnesses were not caused by E. coli, a much more dangerous bacterial infection that has sickened 52 patrons of Chipotle restaurants in nine other states.
Eighty Boston College students reported gastrointestinal symptoms after eating at the Cleveland Circle restaurant, the university said.
“That’s a lot of people to get sick,” said Dr. Anita Barry, director of the infectious disease bureau at the Boston Public Health Commission. Although norovirus causes vomiting and diarrhea every year in Boston, Barry could not recall an outbreak of such magnitude linked to a restaurant in recent years.
The city moved Monday to close the Cleveland Circle Chipotle — a rare emergency measure — after finding three violations, including a failure to keep food hot enough.
William Christopher, commissioner of the city’s Inspectional Services Department, which oversees restaurant health safety, said the Chipotle will not reopen until health officials complete their investigation, inspectors determine corrective measures, and Chipotle makes the necessary fixes.
Chris Arnold, communications director for the Denver-based restaurant chain, said the company is cleaning up the closed outlet.
“In preparation to reopen, we are conducting a full sanitization procedure, surveying our employees to be sure none are sick (as a matter of policy, any sick employees will be held out of work until they are healthy and cleared to return), and working with health officials while they conduct their review of this,” Arnold wrote in an e-mail.
Identifying the culprit germ does not end the disease specialists’ investigation. Boston health officials are interviewing all the Boston diners who got sick, asking what they ate, in the hope of identifying the contaminated food. Ill patrons living outside Boston will be referred to local health authorities or the state Department of Public Health.
Norovirus, notorious for ruining many a cruise, inflames the stomach and intestines, leading to severe vomiting and diarrhea that lasts one to three days. Most people get better without medical help. Health officials said they were not aware of anyone affected by the ongoing outbreak who needed to check into a hospital, although Boston College said some students received outpatient treatment for dehydration at local hospitals.
Norovirus is highly infectious; only tiny amounts of the virus are needed to cause illness. It is the most common cause of food-borne illness outbreaks in the United States. The virus can be transmitted by touching sick people or contaminated surfaces, but in the case of the Chipotle patrons, Barry said, it was caused by ingestion.
“They almost certainly got it by eating it.”
Barry said she had received reports of 65 illnesses linked to Chipotle but expected more cases to come in. All but two or three were Boston College students, she said. She also expects those sickened at the restaurant to continue spreading the disease and urged people to wash their hands well to prevent that.
Boston College spokesman Jack Dunn said 80 students reported to the college health service that they had suffered gastrointestinal illnesses, and all said they had eaten at Chipotle over the weekend. The college notified the city, which sent an inspector to the restaurant.
‘Our most important consideration here is safety and sanitary conditions.’William Christopher, commissioner of Boston’s Inspectional Services Department
The inspector found three serious violations of sanitary rules: Chicken and beef were not kept hot enough; an employee had come to work ill on Thursday; and multiple patrons had reported being sick. Neither Barry nor Christopher had information about the sick employee’s symptoms and could not say whether the worker was connected to the outbreak.
Chipotle is the only restaurant in the city currently under temporary shutdown order; three others were closed this month and last, but they reopened within days.
Christopher did not a have an estimate on when Chipotle might reopen.
“Our most important consideration here is safety and sanitary conditions,” he said. “It’s a matter of getting to the essence of what’s causing this illness and making corrective action.”
Asked whether he intended to inspect other Chipotle restaurants in Boston, Christopher said he had no reason do so now.
“We’re hoping it’s an isolated event at this establishment,” he said.
City records posted online show that the Cleveland Circle restaurant passed its previous two inspections — in April 2015 and in July 2014 — and that no violations were found during those visits. Christopher said the restaurant has not had any major violations since 2008.Matt Rocheleau of the Globe staff contributed to this report. Felice J. Freyer can be reached at email@example.com. Follow her on Twitter @felicejfreyer.