Health authorities are warning that suspected food-borne botulism linked to an Ohio church picnic that killed a 54-year-old parishioner could lead to more deaths among another 18 people who now exhibit symptoms.

"These people are really ill, and the care is supportive," said Dr. Andrew Murry of Fairfield Medical Centre. "Any time somebody has to be on a ventilator for that long a period of time, it's possible they could do badly."

An additional 21 people of the 60 or so who attended the picnic have come forward and are under observation but so far have exhibited no symptoms. Symptoms can appear as long as 10 days after exposure.

Many became ill soon after the Sunday event sponsored by the Cross Pointe Free Will Baptist Church in Lancaster. Officials are reasonably certain the sicknesses are a result of botulism, but won't know for certain until tests on the people and food are completed.

"We've been interviewing patients and family members who were at the event," Jennifer Valentine, spokeswoman for the Fairfield County of Health, told the Lancaster Eagle-Gazette. "We're trying to narrow down the sources of the food and send samples our for testing. There are about 20 things on the list we're looking at."

Botulism is not contagious.

The federal Centers for Disease Control arranged for a shipment of botulism anti-toxin to Ohio from the national stockpile, reports CBS.

Botulism is a rare but serious paralytic illness caused by a nerve toxin produced by the bacteria Clostridium botulinum. Symptoms include blurred or double vision, drooping eyelids, difficulty swallowing and shortness of breath.

Pastor Bill Pitts said parishioners are trying to help with clues to the source. "Everyone is trying to find the common thread," he said. "My heart is crying, and I pray for the people and their families."

A note on the church's web site offers thanks for "all the prayers and sympathy at this time," adding: "Please remember God is good, the Great Physician and our comfort!"