KETCHIKAN — State scientists looking into paralytic shellfish poisonings in southeast Alaska have found the highest levels of toxin ever recorded, so high that just one mussel could cause death in several people.

Scientists with the state Section of Epidemiology are looking into the illnesses of more than a dozen people since May after developing symptoms of PSP.

Two men with suspected PSP were admitted to a local hospital in Ketchikan on Wednesday. The two men both had symptoms of PSP after eating mussels harvested from nearby Rotary Beach.

Tests showed that baby mussels taken May 25 from a boat dock in Ketchikan had toxin levels estimated at more than 30,000 parts per million, according to the Alaska Department of Health and Social Services.

“At those levels, a single mussel is enough to kill several people,” said Kate Sullivan, a member of the Alaska Harmful Algal Bloom program at the University of Alaska Southeast.

Shellfish is considered toxic if it contains more than 80 parts per million of the toxin.

Scientists testing mussels around Ketchikan found levels above 5,000 parts per million. Toxin levels were up to 2,000 parts per million in butter clams and more than 1,100 parts per million in cockles.

The Ketchikan Daily News reported Wednesday that five people on Annette Island developed symptoms last week. One man was hospitalized in intensive care Friday after eating cockles. The man has recovered.

Public health officials continue to urge people not to eat recreationally harvested shellfish such as cockles, clams, mussels, oysters and scallops. Epidemiologist Kim Porter said they are not considered safe any time of the year.

Early symptoms of PSP can include tingling of the lips and tongue. That can progress to tingling in the fingers and toes, and later, a loss of control of arms and legs, followed by difficulty breathing. Death can occur within two hours.

Warning signs about PSP have been posted in Metlakatla on Annette Island at local stores, the post office, popular beaches and boat launches. Police also are making announcements on maritime radio.