A three-month investigation into a gastro outbreak at the MCG on Anzac Day has found the "most likely" cause was a relish.

Key points: The investigation has not produced any "definitive results" on what caused the gastro outbreak

The investigation has not produced any "definitive results" on what caused the gastro outbreak But Victoria's chief health officer said people who had eaten the relish were 12 times more likely to fall sick

But Victoria's chief health officer said people who had eaten the relish were 12 times more likely to fall sick The relish was served to guests at the MCG lunch alongside a rabbit, chicken and pork terrine

A rabbit, chicken and pork terrine was originally suspected as the cause of the outbreak but Victoria's chief health officer Brett Sutton today said the relish that the entree was served with was the more likely cause.

"After three months of investigation, which included extensive testing of implicated foods and ingredients, there were no definitive results as to the specific cause of illness," Dr Sutton said.

"The evidence gathered during the investigation, however, revealed that the most likely source of illness was the relish which was served with the entree of rabbit, chicken and pork terrine."

Dr Sutton said people who ate the relish were 12 times more likely to become unwell than those who did not.

"The signal coming from the relish was very strong," he said.

"The relish was likely contaminated with something.

"The very dramatic presentation with lots of people feeling faint and dizzy and vomiting within half an hour, or a couple of hours, really points to it being a toxin carried on that food."

The investigation identified 37 patrons and one staff member who became sick with a range of symptoms including acute gastroenteritis after attending the president's lunch in the MCG's Olympic Room on April 25.

Several people were assessed by paramedics at the ground and seven were taken to hospital.

They were treated in the emergency department and then sent home.

Outbreak just 'bad luck'

The investigations included testing samples from the terrine and the ingredients used to make the relish.

The evidence indicated the illness was more likely to have been due to consumption of food rather than as a result of chemical or other environmental exposure.

Health Department officers also interviewed 109 guests and staff who attended or worked at the function.

"As this was an isolated incident and no issues were found with food processes, there is no ongoing risk to the public and no further action is required," Dr Sutton said.

"It's just one of those awful things."

He said it was not unusual for this type of investigation to be inconclusive.

"Ultimately we have to put it down to bad luck. They probably received food that had a toxin on it," he said.

"It went through a process of having boiling water added to it to make the relish but toxins can survive above 100 degrees Celsius.

"That's tricky to manage but it is worth everyone thinking about the possibility of that when they have food come through kitchens."

Dr Sutton said the event organisers had cooperated with the investigation and the case was a warning that food contamination could happen in any context.

Tickets for the president's lunch and game cost $725.

In a statement, the Melbourne Cricket Club said additional precautionary measures have since been implemented.

"Food items associated with the function's entree have not been served at the MCG since the incident, including the suspected item identified by the [Department of Health and Human Services] as the most likely source of illness," the statement said.

"We are deeply disappointed that this incident occurred and express our sincerest apologies to those patrons affected."