Food safety experts traced the salmonella outbreak to Wright County Egg, near Galt, Iowa, which is one of two companies whose eggs are believed to have been contaminated. More than 500 million eggs have been recalled.
Federal investigators said salmonella samples found in chicken feed and manure found at Wright County Egg in Iowa matches the strain of salmonella that has sickened people across the country.
As investigators turn up more clues, the number of people thought to have been made ill by bad eggs is expected to grow.
Centers for Disease Control and Prevention officials say they normally see around 900 cases of salmonella from May through August each year. But since May, the number of cases has soared to more than 2,400.
The upshot: nearly 1,500 people so far have likely been infected with salmonella from contaminated eggs. No deaths have been reported.
It's the largest outbreak of this nasty gastrointestinal illness since the agency began keeping tabs in the 1970s. See the CDC's latest information about the outbreak here.
The CDC and Food and Drug Administration have been investigating the uptick in salmonella cases since July, eventually tracking the cases back to eggs from Wright County Egg and Hillandale Farms.
The two companies' recalls have affected more than half a billion eggs.
Hillandale gets feed and young chickens from Wright County, which is at the center of the government's investigation. "We consider the current identified sources as responsible for the cases we're seeing," said the CDC's Dr. Christopher Braden said in a media briefing today.
But in the same call, FDA Associate Commissioner Joshua Scharfstein cautioned, "The feed facility could actually just be part of the general contamination through the farms," noting it could come into facilities through rodents or other birds.
Meanwhile, Democratic Rep. Henry Waxman of California has asked top officials at both egg facilities to testify before his committee next month.