The mysterious illness that led to the costly closure of Heston Blumenthal’s famed Berkshire restaurant The Fat Duck was possibly caused by norovirus, according to the chef.

Speaking to Hospitality magazine after arriving in Australia today for the Melbourne Food and Wine Festival, Blumenthal said that after exhaustive tests at the restaurant, of the staff and of customers, norovirus was the only potential cause that had been found.

Blumenthal made the decision to close down the three Michelin star restaurant last month after it received a series of calls from customers who said they had been ill after eating there and got in contact with the Health Protection Agency and told them what had happened. The restaurant was reopened last week after two and a half weeks.

He said he was shocked that anything could have gone wrong because of the stringent food safety measures that are in place at the restaurant.

“It is categorically not food poisoning, we know that,” Blumenthal said. “For the last five years we’ve been sending food off every month for sampling and I don’t know any other restaurant in the country that does that. We also have a company that has been looking after all our health and safety stuff for the last five years.

Blumenthal said that since the closure of the restaurant 200 tests had been done on food processes, as well as tests on all of the staff and 80 swabs of the environment, and all had been negative on all counts of food poisoning or hygiene issues. “The only thing that has come up is that three staff and five customers have been tested positive for something called norovirus,” he said.

Blumenthal said support for the restaurant throughout the crisis had been “incredible”. “It’s affected the restaurant big time because had to cancel 800 people because of the closure but in terms of the business and people wanting to come in then no,” he said.

Blumenthal will be appearing as part of the Langham Melbourne Masterclasses program that is a key part of the Melbourne Food and Wine Festival. His two sessions—one on his own and the other sharing the stage with Thomas Keller, and both moderated by Neil Perry—were early sell outs.

For information on the festival head to melbournefoodandwine.com.au