INDIANAPOLIS -- A Castleton-area restaurant was closed indefinitely Friday over reports that more than 300 people became ill and three people were hospitalized after eating there recently, Marion County Health Department spokesman John Althardt said.

Friday's decision to close the Olive Garden restaurant on Indianapolis' northeast side came after health officials started hearing of illnesses in people who ate there Wednesday -- the day that the department, having started checking illness reports from people who dined there over the weekend, said that the restaurant took remedial measures and appeared to be a safe place to eat.

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Video: Indy Restaurant Closed As Illness Reports Reach 300
Video: Health Official Explains Closing

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The ill told health officials they ate at the Olive Garden between Saturday and Wednesday. They reported flu-like symptoms, including vomiting, diarrhea, nausea and fever, 6News' Stacia Matthews reported.

Health officials said the sick include some Olive Garden employees who worked Saturday, Sunday and Monday. Six of them called in sick on Monday, officials said.

The health department's Ed Culver said the latest illness reports came even after the restaurant took remedial steps like thorough cleaning and ensuring that ill employees were off the job.

"So, we thought that this would be an opportunity to suspend operations (at the restaurant). Olive Garden agreed with that," Culver said. "They're going to do additional cleaning in the restaurant, and that way there won't be any employees present or patrons coming in and out. And we'll reassess the situation on Monday."

State Health Department: Norovirus May Have Been Cause

Health officials said they still were trying to identify the illness and the cause, but the state health department said that a prime suspect is gastroenteritis, possibly caused by norovirus.

"You've probably heard about the illnesses on the cruise ships. This is the same type of thing, possibly. The investigation is still ongoing," the state health department's Scott Gilliam said Friday.

Gilliam said norovirus spreads from person to person easily.

"Just by going out to a place to eat or visiting friends, you can contract the illness pretty easily, and it mimics food-borne illness," he said.

Investigation Began Tuesday

MCHD officials began an investigation Tuesday, inspecting the restaurant and reviewing its food-handling procedures. On Wednesday, Culver said the restaurant took follow-up measures and said it was safe to eat there.

Investigators have been recording what the ill customers ate and collecting stool samples for analysis.

By Wednesday, 19 customers had reported to health officials that they were ill. By Thursday, the number of people who reported illness rose to 165.

Because some of the sick are residents of Hamilton County, the health department in that county also is investigating.

Health officials asked that anyone who became ill after eating at the restaurant should contact the Marion County Health Department at 317-221-2222 or the Hamilton County Health Department at 317-776-8500.

Stay with 6News and TheIndyChannel.com for updates.