DILLINGHAM -- A botulism outbreak in Bristol Bay communities is being monitored by state and local health officials, according to the state Department of Epidemiology, which said Wednesday that more than 25 people have so far been linked to a batch of contaminated seal oil produced in the village of Twin Hills.

Several people have been hospitalized, some are being monitored and health officials are still trying to contact others.

The first botulism cases were reported Friday after two people were flown from the village of Quinhagak to Bethel for care. The two were later taken by medevac to Anchorage and remained on respiratory support Wednesday, reportedly unable to breathe on their own, according to a state official monitoring the outbreak.

Three others from Quinhagak were treated for symptoms of botulism, and others in Twin Hills and Dillingham have reported symptoms or are being monitored. One child has also shown symptoms of the disease, which can be fatal, according to Dr. Michael Cooper, the infectious disease program manager at the Department of Epidemiology.

"This is a very concerning outbreak," said Cooper. "This is one of the largest clusters of botulism we've ever seen."

An investigation linked the illnesses to a batch of seal oil produced in Twin Hills, and Cooper said testing conducted at a state lab revealed the oil was particularly toxic.

"When it was tested, it came back at the highest level the lab instrument can measure for botulinum toxin," he said Wednesday.

The testing was completed Tuesday, and Wednesday morning, the state dispatched a second public health nurse from Anchorage to continue the investigation out of Dillingham.

"In an odd twist to this case, after we showed preliminary test results to the family who produced the oil, they sort of refused to stop eating or serving it," said Cooper.

The state did not have further details Wednesday about where that batch of seal oil may have been sold or traded in the region.

Botulism is a paralytic illness caused by the Clostridium botulinum bacteria. In Alaska, botulism occurs almost always in fermented or preserved foods like improperly canned fish and "stink heads," according to a 2011 report from the Alaska Department of Health and Social Services. According to state data, seal oil appears to be one of the main culprits behind botulism cases in Alaska, responsible for 54 outbreaks from 1950 to 2010.

"Botulism can be lethal," said Dr. Catherine Hyndman, a family physician at the Kanakanak Hospital in Dillingham, where staff were helping track and treat infected individuals. "But one of the big problems, as many know, is that botulism toxin does not necessarily smell or taste out of the ordinary. The food can look and seem to be perfectly normal, but yet be contaminated."

Early symptoms may include nausea and gastrointestinal distress such as vomiting, diarrhea and abdominal pain. According to Hyndman, early signs of muscle paralysis are indicative of botulism.

"This is a poison that paralyzes the muscles," she said. "The smallest muscle is the muscle that moves the eye to the sides, to the right or the left, and oftentimes that is the first muscle that is paralyzed." Blurred or double vision, unreactive pupils or drooping eyelids can be a sign of botulism poisoning.

Symptoms may appear as early as one day or as late as 10 days after consumption of contaminated food. Health officials are urging those who may have eaten some of the contaminated seal oil to seek medical advice and perhaps plan to be near a medical care facility for observation.