State and local fisheries officials said Thursday that toxic bacteria in oysters caught in shallow waters off Wellfleet do not present a similar threat to Vineyard oysters, but nevertheless urged shellfishermen in all coastal areas to take precautions, including refrigerating oysters as soon as possible after catching them.

The recommendations come in response to the discovery that five people last year became ill from oysters that contained the bacteria vibrio parahaemolyticus, or VP, as it is known on the waterfront. In large amounts in an oyster, it can cause gastrointestinal illness.

As a result of those cases, the Federal Food and Drug Administration (FDA) ordered the state Division of Marine Fisheries and the state Department of Public Health to come up with a plan. The agencies held two meetings recently with local oyster growers and handlers as part of their response. As part of those meetings the state agencies called for uniform refrigeration of oysters, particularly “in Eastern Cape Cod Bay, from Barnstable to Provincetown,” said J. Michael Hickey, chief shellfish specialist for the state Division of Marine Fisheries.

Mr. Hickey said the bacteria are known to be most harmful during the hot summer months when the temperature of the water gets up to the 80s. The commercial oyster fishery off Wellfleet and other areas of Cape Cod Bay takes place mostly in a tidal zone that rises and falls as much as four feet in the bay. Oysters are frequently exposed to the hot air and that helps the bacteria. To mitigate the growth of the bacteria, Mr. Hickey said the oyster growers must take steps to bring their harvest into refrigeration within five hours of pulling them out of the water. He said the plan is to get the temperature of the oysters down to 50 degrees within ten hours of harvest.

The concern does not affect Vineyard commercial oyster growers directly, Mr. Hickey said, primarily because the Vineyard product is raised underwater and not on tidal flats. Most of the Vineyard oysters are raised suspended in the water column of Katama Bay and Menemsha Pond and are not generally exposed to the high temperatures found in shallow areas of Cape Cod Bay and other regions. But he and other officials said the harm to humans is preventable. They recommend refrigeration, regardless of the location of the shellfish.

Rick Karney, director of the Martha’s Vineyard Shellfish Group, said the VP bacterium is fairly ubiquitous. But when exposed to hot summer weather for long periods of time, the bacteria grow and become harmful to humans. “As long as fishermen stick to their best management practices, we should be okay,” Mr. Karney said. Any oyster shellfisherman who leaves his catch out in the sun on a hot summer day for extended periods of time is inviting trouble, he said.

Normally the wild oyster fishery is open only during the winter months. But those who raise cultured oysters are allowed to harvest and market their product year-round.

There were two cases in July that came from restaurants in Dennis. There were an additional three cases that arose out of oysters eaten at the Wellfleet Oysterfest in October.