An outbreak of food poisoning in Whangarei is being linked to one food outlet.
Nine out of 11 people who have tested positive for the strain of salmonella infantis have eaten at or bought food at the undisclosed business. The other two cases were possibly picked up through secondary contact. Health officials are not naming the food outlet at this stage.
With cases expected to spread rapidly through secondary contact that number could be the tip of the iceberg, Northland Medical Officer Claire Mills said.
"We had 11 confirmed cases of salmonella infantis which is quite a cluster of a strain not particularly common in Northland, and nine seemed to be linked to one eating premises," Dr Mills said.
Health officials are investigating the eatery and its food supply chain to find a possible source of the bacterial infection but have not been able to find whether it came from a product or was spread by an infected person.
The infantis strain is often connected to chicken and eggs but that does not appear to be so in the Whangarei case.
Dr Mills said officials had found the business to be clean and have good food handling practices. Because of the type of strain, it was likely the infection had been introduced in a food item or product made somewhere else.
Dr Mills is urging people who experience stomach upsets and/or diarrhoea to be careful with hand and food hygiene. It was likely the illness had now spread further through the community in "second stage" of infection.
The infection causes diarrhoea for four to five days, stomach pains and sometimes vomiting. Anyone with very severe symptoms should go to their doctor. People with immuno-repressed conditions, the elderly and very young are likely to suffer the worst effects. Most people develop diarrhoea, fever, and abdominal cramps 12 to 72 hours after infection.
"The cases we have seen have been people sick enough to seek medical attention but there will be many more with this," Dr Mills said.
"Any of these things that come to our attention are usually under-representative of how much is going around."
Salmonella bacteria can survive for some time without a host.