While the worst could be over, investigations are continuing into the source of last month's paratyphoid outbreak, including how shellfish in the Napier Marina were contaminated.

Over the course of the outbreak the number of cases of the typhoid-like illness rose to 10 with the last confirmed on September 25. One patient required hospitalisation in Auckland.

Hawke's Bay District Health Board medical officer Rachel Eyre said there was a possibility of further cases, "but it is likely we are over the main peak of new cases".

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The illness has been linked to mussels collected from Ahuriri and consumed at two tangi in August and September.

The investigation is ongoing, with the DHB working with other local agencies.

"The results from shellfish, so far, obtained from Ahuriri Port, suggest human faecal contamination. We are working to determine how that contamination occurred".

Napier City Council director infrastructure Jon Kingsford said a sampling programme had been undertaken to assess the levels of indicator bacteria - including E.coli - in the marina and wider estuary.

"We have also started the process of surveying all berth owners in the marina to determine how many people use the boats, live on the boats and what their movements have been in the past few months," he said.

So far no sources had been identified from water testing.

"However, ESR has suggested that the source of mussel contamination is human sewage. It is hoped that the survey of berth owners may provide some useful information."

The Hawke's Bay Regional Council has also been involved in the investigation, with staff monitoring alongside the city council, and supplying this data to the Public Health Unit.

The HBDHB was also working with the Ministry of Health, Ministry for Primary Industries, the Institute of Environmental Science and Research (ESR), local kaumātua and Māori Health providers (including the DHB Māori Health Team).

Shellfish from Ahuriri were at a high risk of contamination due to pollutants from being close to the city, overflow, as well as boats nearby, which might illegally discharge sewage into the water.

The public were reminded to heed warnings and not eat any shellfish gathered from the Napier Marina area. They were also asked to report any discharges they notice within the marina.

Anyone who might have been contaminated was advised to seek medical advice as the illness can present itself without symptoms.

Paratyphoid generally occurs within 10 days of consuming contaminated food or water but symptoms may take as long as four weeks to develop.

Most people with paratyphoid would have a fever, chills, headache, possibly a rash and might also have severe vomiting and diarrhoea.