Island Health and the First Nations Health Authority are warning people not to eat herring eggs after linking them to confirmed cases of cholera on Vancouver Island.

The intestinal illness — which can cause nausea, vomiting and severe watery diarrhea — is most commonly found in travellers returning from endemic regions.

The cases on Vancouver Island have caught health officials off guard.

"It's definitely something we're taking seriously," Dr. Shannon Waters, a medical health officer with Island Health, said on CBC's On the Island.

The advisory applies to herring eggs found on kelp, seaweed and other surfaces and harvested in the area from French Creek to Qualicum Bay.

Investigation underway

Waters said "less than a handful" of cases were discovered after stool cultures from sick patients came back positive for cholera.

All patients were First Nations and had consumed herring eggs, she said.

The patients suffered from nausea and diarrhea, but Waters cautioned that some infected people may not show symptoms.

An investigation is underway with First Nations communities and the B.C. Centre for Disease Control.

Officials are testing marine water and leftover food samples and assessing the handling and distribution of herring eggs.

"It certainly makes us curious about the marine environment," Waters said, citing factors such as sewage, boat traffic and rising temperatures.

"Our health is connected to it and this is evidence of that."

First Nations are 'concerned'

Herring eggs are a traditional food source for First Nations, who associate it with the coming of spring.

The eggs, which are a source of protein, are sticky when they spawn and adhere to surfaces such as seaweed or kelp.

First Nations on the island are concerned about the cases, said Waters, who is Coast Salish.

"It ... creates some sadness because people had been looking forward to this, especially a lot of elders who grew up eating this food a lot more."

The harvesting of herring eggs is not regulated, Waters said, and is a process that is passed down among family and friends.

The advisory cautions people to wash their hands after using the bathroom and caring for someone who is ill and to discard any extra stored herring eggs.

With files from CBC's On the Island