The cause of the illness among diners at the Hellenic Republic restaurant in Kew has been identified as a viral infection likely to have been spread by a member of the kitchen staff, according to the Victorian Department of Health.
Celebrity chef George Calombaris and partners shut the Cotham Road restaurant for 24 hours earlier in May after the Department of Health and Boroondara Council received reports that many patrons who had eaten there on Mother's Day (May 11) had experienced symptoms including vomiting, diarrhoea and stomach cramps.
Health Department spokesman Bram Alexander said norovirus - a common, highly contagious cause of gastroenteritis - had been identified as the culprit in tests performed by the department.
"Of the 300-plus diners we interviewed, around 90 reported illness, which could have been associated with eating at Hellenic Republic Kew," Mr Alexander said.
He said the virus "was likely to have come from an infected food handler at the restaurant".
"While no specific food handler at the premises was identified as being ill at work, the local council is working with the restaurant to reinforce safe food handling practices, and the importance of good personal hygiene."
Following Boroondara Council inspections, Hellenic Republic Kew was shut on Friday May 16th, re-opening the following day.
A spokeswoman for Mr Calombaris' company, Made Establishment, said the group was continuing to work with the Department of Health to "identify how this virus entered our venue and to avoid any future issues".
"A full deep clean has already taken place to ensure the restaurant is norovirus-free, and the Department of Health is happy for us to return to full and normal trading."
Mr Calombaris issued a statement saying his Kew team had been "absolutely devastated" by the outbreak.
"I am so sorry for those poor people that have been affected and to those inconvenienced by us taking precautionary measures and closing down the venue,” he said.
"We are confident in our procedures and standards of hygiene and the welfare and enjoyment of our guests has always been and will continue to be our highest priority."
Calombaris owns a 25 per cent stake in Made Establishment, which also controls Hellenic Republic in Brunswick and The Press Club and Gazi in Melbourne CBD.