Shellfish consumed at a Hastings tangi is believed to be linked with cases of paratyphoid being investigated by the Hawke's Bay District Health Board.
There have been four confirmed cases of paratyphoid fever, all of which have needed hospital treatment. The health board is following up three suspected cases.
A board spokeswoman said at least two of the cases ate mussels gathered from Napier's Ahuriri area.
There was also concern mussels from the same area may have been eaten at a tangi at the Tangoio Marae, 11 days ago.
This was the tangi for former Hastings resident Vincent Taurima, who was one of two men found in Tongariro National Park after an extensive four-week search by police. Mr Taurima's death has been referred to the coroner.
Tangoio Marae chair Lewis Neera - who had not gone to the tangi - said they had been advised about a "potential serious outbreak" of the fever among tangi attendees.
They had been told to advise any attendees who thought they might be suffering from paratyphoid to immediately be tested, "even though you think you may have recovered" as the fever can be passed on to others.
Medical Officer of Health Nick Jones said paratyphoid was a serious illness and a notifiable disease.
"It is most important people get medical care or call HealthLine if they are unwell."
People with the disease will have a fever, chills, headache, possibly a rash and may also get severe vomiting and diarrhoea.
Paratyphoid generally occurs within 10 days of consuming contaminated food or water but symptoms may take as long as four weeks to develop.
Dr Jones said the district health board had teams in the community working to follow-up with anyone that was sick, but the most important thing was to get medical help if sick.
"People with paratyphoid can carry the bacteria in their blood and in their stomach and gut so it is possible for it to be passed on through faeces," he said.
"Hand washing was extremely important to help prevent infecting other people as you can get paratyphoid if you eat or drink things that have been handled by a person who has the bacteria."
Anyone feeling sick and who consumed shellfish or has been in contact with anyone who had eaten shellfish from the Napier Marina should contact their family doctor or they could call HealthLine 24/7 0800 611 116.
More information on how to protect yourself and others is available from here