Most of those who fell ill had eaten takeaway food

The outbreak appears to centre on two takeaway restaurants in the area, North East Lincolnshire Council says.

With nine cases at the weekend and four on Monday, environmental health officers believe it has peaked.

Once their investigation is complete, officers will decide whether to mount any prosecution, the council said.

Relatively rare

Initial investigations focused on just one takeaway outlet but now officers say they are looking at a second.

Environmental health team divisional manager Steve Mercer said: "We do believe there is no ongoing risk to the public from takeaways in the area."

"We do believe there is no ongoing risk to the public from takeaways in the area." Environmental health team divisional manager Steve Mercer

"We are looking at possible areas in common between the two principal sources of the outbreak, such as suppliers," said Mr Mercer.

"I am hopeful that by the end of the week we will be getting to the bottom of it."

He said relatively rare Salmonella Newport strain appeared to be involved in this outbreak, which could make it easier to trace its source.

"There are usually only about 150 cases of this strain reported throughout the UK every year.

"To get as many as we have had in our area is quite unusual."

The last outbreak of comparable size in the area was in 1996 when 150 people were infected. That outbreak led to the prosecution of the owners of a sandwich shop in Grimsby town centre.

Symptoms of salmonella food poisoning include abdominal pains, diarrhoea and vomiting, and usually develop between 12 and 72 hours after the consumption of affected food.