WASHINGTON – Botulism poisoning from commercially canned foods has been virtually eliminated in the United States, making the new cases linked to hot dog chili sauce all the more striking.

On Thursday, the Food and Drug Administration, Agriculture Department and Centers for Disease Control and Prevention were investigating a Castleberry’s Food Co. plant in Augusta, Ga., where the suspect product was canned. An equipment malfunction may be responsible for the contamination, the Agriculture Department said.

Four people have been hospitalized; they are expected to survive.

Botulism is a muscle-paralyzing disease caused by a toxin made by a bacterium, Clostridium botulinum. Such bacteria are commonly found in soil.

Typically, commercially canned foods are heated long enough and to high enough temperatures to kill the spores that otherwise can grow and produce the toxin. If canned foods are underprocessed, the bacteria can thrive in the oxygen-poor environment inside the sealed containers.

Food packaged in defective cans, including those with leaky seams, can become contaminated because the bacteria can be sucked into the containers as the product cools, according to health officials.

Indeed, the company experienced a production problem about two months ago, when cans were being overheated _ which can cause them to expand enough to allow in contamination _ before being cooled, spokesman Dave Melbourne said. Production was halted until the foods being canned at the time could be checked. Those checks found no problems, Melbourne added.

Each year, the CDC records roughly 25 cases of foodborne botulism poisoning. Most involve home-canned foods. Some fermented whale and other traditional foods prepared by Alaska natives also have been implicated in outbreaks.

CDC medical epidemiologist Dr. Michael Lynch said the last U.S. case of botulism linked to commercially sold canned food dates to the 1970s.

One food safety expert said the new outbreak was disturbing.

“It raises concerns that the existing food safety programs that have been functioning are losing ground because of gaps in FDA oversight,” said Caroline Smith DeWaal, director of food safety for consumer group Center for Science in the Public Interest.

The FDA’s Dr. David Acheson, the agency’s lead official on food safety, called the outbreak a rare event.

“Things you can have a great deal of faith in can fail. Mistakes can happen. The critical part is when mistakes happen, the federal agencies get alerted quickly and react to them and contain the problem,” Acheson said.

Symptoms of botulism include double or blurred vision, drooping eyelids, slurred speech, difficulty swallowing, dry mouth and muscle weakness that moves down the body. Eventually, paralysis can cause a person to stop breathing and die, unless supported by a ventilator. Botulism is fatal in about 8 percent of cases; most victims eventually recover after weeks to months of care.

Botulinum toxin is extremely potent. Even opening a contaminated can may expose consumers to the toxin if it is inhaled, swallowed or absorbed through the eye or breaks in the skin, health officials said.

Yet small doses of an FDA-approved product made from the toxin are routinely used to paralyze or weaken the muscles that can cause facial wrinkles. The product is best known by its trade name: Botox.

The FDA warned consumers to throw away 10-ounce cans of Castleberry’s, Austex and Kroger brands of hot dog chili sauce with “best by” dates from April 30, 2009, through May 22, 2009. Castleberry’s, owned by Bumble Bee Seafoods LLC, has recalled the products flagged by the FDA, as well as seven others produced at the same time.

Associated Press medical writer Mike Stobbe contributed to this report.

On the Net:

Castleberry’s Food Co. recall information: http://www.castleberrys.com/

CDC botulism information: http://www.bt.cdc.gov/agent/botulism/index.asp

A service of the Associated Press(AP)