Health officials in Pudong have closed the cafeteria on the construction site of the Citigroup Tower on Huayuanshiqiao Road after about 100 workers complained of stomachaches and diarrhea on Thursday night.
Forty-seven workers were sent to hospital yesterday morning. They had all been released by yesterday afternoon.
"We have collected food samples and conducted research, and the results will be available in five to seven days," said an official surnamed Shi with the Pudong New Area Health Supervision Agency.
"So far, we only can say it is suspected of being a food poisoning case."
He said health officials checked the construction site recently and no serious problems were found at that time.
"The symptoms are similar to food poisoning," said Xiang Peijun of Shanghai East Hospital, where many of the workers were treated.
Doctors from Shanghai Gongli Hospital said they treated five patients yesterday morning.
"We are not clear about the cause right now," said Gu Wei, director of the hospital's infectious disease department. "All patients left in the afternoon after receiving treatment."
A worker at the site said about 70 workers from his decorating team felt sick after eating in the cafeteria at the site on Thursday night.
"Some of them were sent to hospital this morning and others just took medicines from the site's clinic," the worker said.
"Summer is the peak time for food poisoning, while the agency has taken various efforts to enhance inspection and monitoring," said Shen Xian, an official with the Pudong health agency.
"If it is food poisoning due to improper operation, the site authorities may face a fine of no more than 50,000 yuan (US$6,024) and be required to renovate the cafeteria," Shen said.