Sixty people were hospitalized Sunday night after eating a turkey dinner at a Denver homeless shelter, marking the largest food poisoning outbreak at a U.S. shelter in the past decade, according to the National Coalition for the Homeless.

"I would say this is something that is out of the norm for sure," said the coalition's executive director, Neil Donovan.

The first food poisoning victim went to the hospital at around 7 p.m., said Alexxa Gagner, a spokeswoman for the Denver Rescue Mission, an overnight homeless shelter that serves three meals a day. "Folks were getting very sick when I arrived on the scene at around 9," Gagner told ABCNews.com.

First responders closed off the block, and victims rode in ambulances two-by-two, said homeless shelter resident Robert Fanoele, 28.

In all, 52 people were transported to a nearby hospital directly from the shelter, and eight more were transported to a hospital from Samaritan House, another local shelter, said Meghan Hughes, the city Department of Environmental Health spokeswoman. The food poisoning victims had all eaten at the Denver Rescue Mission, she said.

Fanoele, who joined the shelter's resident program on Saturday, sat down to dinner at about 5:30 p.m. Sunday.

"Right around 7 o'clock, we started doing dishes and immediately after that, I felt a few sharp pains," he said.

Fanoele became sick, and three hours later, he was lying in the back of an ambulance on his way to the hospital.

He was treated and returned to the shelter at 1:15 a.m. Today, he feels better, he said.

"I'm doing good," Fanoele said. "I'm still feeling a little nauseous and a little weak."

It is not yet clear whether the turkey or another food item caused the outbreak, Hughes said.

Although the decades-old shelter serves 600,000 meals a year, Gagner said it has never had a food poisoning outbreak before. She said the shelter's kitchens are held to the same standards as restaurant kitchens, but it also accepts food donations from several local catering companies.

Donovan, who heads the National Coalition of for the Homeless, said he used to run a homeless shelter in the 1980s, when shelter food safety standards were more lax.

"When I first started back in 1980, food would come in, and you basically took it and heated it and put it out. That was a very normal practice, and now that just isn't the case anymore," he said. "The Rescue Mission has a fairly sophisticated donation program."

Abby Davisdon, a health investigator for the city, told ABCNews.com that two investigators from city Department of Environmental Health and two epidemiologists were at the shelter Monday morning, asking questions about food safety practices and the menu.

Investigators will want the full list of symptoms from those who became ill and a list of anything else they might have eaten on Sunday, Davidson said.

Davidson said the only symptom she'd heard about was vomiting.

Seven people who were hospitalized in the outbreak have been released and returned to the shelter, Gagner said.