Government scientists struggled Thursday to pinpoint the source of the first U.S. salmonella outbreak linked to peanut butter, the kid favorite packed into millions of lunchboxes every day.
Nearly 300 people in 39 states have fallen ill since August, and federal health investigators said they strongly suspect Peter Pan peanut butter and certain batches of Wal-Mart's Great Value house brand -- both manufactured by Conagra Inc.
Shoppers across the country were warned to throw out jars with a product code on the lid beginning with "2111," which denotes the plant where the peanut butter was made.
How the bacteria got into the peanut butter was a mystery. But because peanuts are usually heated to high, germ-killing temperatures in the manufacturing process, government and industry officials said the contamination may have been caused by dirty jars or equipment.
"We think we have very strong evidence that this was the brand of peanut butter. Now it goes to the next step of going to the place where the peanut butter was made and focusing in on the testing," said Dr. Michael Lynch, an epidemiologist at the Centers for Disease Control and Prevention.
The recalled peanut butter was produced by Conagra at its only peanut butter plant, in Sylvester, Ga., federal investigators said.
Conagra said it is not clear how many jars are affected by the recall. But the plant is the sole producer of the nationally distributed Peter Pan brand, and the recall covers all peanut butter produced by the plant from May 2006.
Food and Drug Administration inspectors visited the now-shut-down plant Wednesday and Thursday to try to pinpoint where the contamination could have occurred. The FDA last inspected the plant in 2005. Testing was also being done on some of the salmonella victims' peanut butter jars.
Salmonella sickens about 40,000 people a year in the U.S. and kills about 600. It can cause diarrhea, fever, dehydration, abdominal pain and vomiting.
The only known salmonella outbreak in peanut butter -- in Australia during the mid-1990s -- was blamed on unsanitary plant conditions.