Food and Drug Administration officials said Monday that there is no evidence a massive outbreak of salmonella in eggs has spread beyond two Iowa farms, though a team of investigators is still trying to figure out what caused it.

FDA officials said they do not expect the number of eggs recalled — now at 550 million– to grow.
Dr. Jeff Farrar, FDA’s associate commissioner for food protection, said 20 FDA investigators are at the two farms, Wright County Egg and Hillandale Farms, and could be there until next week. He said preliminary findings  should be available this week.

Farrar said the chicks that came to the farms from a Minnesota hatchery appear to have been free of illness, so contamination most likely happened at the Iowa locations. The FDA is looking at eight sites on the farms where laying hens were reared as well as other locations, he said.

The House of Representatives Energy and Commerce Committee said it is investigating the outbreak and sent letters to both farms asking for detailed information about operations, communications with the government and what they knew and when.

The number of illnesses, which can be life-threatening, especially to those with weakened immune systems, is expected to increase. The federal Centers for Disease Control and Prevention has said there could be as many as 1,300 salmonella illnesses linked to the eggs. The CDC said that for every case reported, there could be 30 or more unreported .

Dr. Christopher Braden, a CDC epidemiologist involved in the investigation, said there have been 40 more cases reported since last week, but it isn’t clear whether all are linked to tainted eggs. Braden said the agency has not identified additional clusters of illness that would indicate the outbreak has spread beyond the two Iowa farms.