MPI was informed of the outbreak by the Northland District Health Board on January 20, though it was largely over as no new cases had been reported after January 22.
The outbreak was identified as part of routine surveillance of salmonella cases, Mr Orr said.
Salmonella is a group of bacteria that can cause salmonellosis, which is a type of food poisoning. Typical symptoms include diarrhoea, abdominal pain, vomiting, nausea and fever lasting one to seven days.
Because the investigation did not find the source of the outbreak there was no public warning as there was no way to tell people how to prevent themselves from becoming ill, Mr Orr said. "A number of areas for improvement were identified and follow-up visits by MPI to the bakery confirmed that these improvements had been implemented."
The recommendations mainly involved sanitising preparation and serving surfaces after they had been cleaned.
"Surfaces were being cleaned with detergents and de-greasers. Investigators recommended that sanitisers were used as a final step in cleaning to kill any potential bacteria."
The bakery would be subject to ongoing routine inspections by council environmental health officers.
Northland District Health Board was unable to say how many cases required hospital admission by edition time.
The agenda of a NDHB meeting, which called it a "major outbreak", said there were cases reported in Northland, Auckland and other regions. Other agencies involved in the investigation were Kaipara District Council, the Institute of Environmental Science and Research Limited and Auckland Regional Public Health Service.
The last serious outbreak of food poisoning in Northland was in Whangarei in May 2013. In that instance officials were also unable to pinpoint the source of the outbreak which infected 11 people.
