WASHINGTON (AP) — 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 — 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 of the investigation should be available later 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 different sites on the farms where laying hens were reared as well as other locations, he said.

The House Energy and Commerce Committee said it is investigating the outbreak and sent letters to both farms asking for detailed information about company operations, communications with the government and what they knew and when. Rep. Rosa DeLauro, D-Conn., head of the spending committee that oversees the Agriculture Department and the FDA, sent the two government agencies a letter asking what they knew.

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 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 cases.

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 immediately clear if all are linked to tainted eggs. Braden said so far the agency has not identified additional clusters of illness that would indicate the outbreak has spread beyond the two Iowa farms.

As her agency investigates the cause, FDA chief Margaret Hamburg said the FDA hasn’t had enough authority to help prevent outbreaks.

Hamburg said Congress should pass legislation stalled in the Senate that would increase the frequency of inspections and give the agency authority to order a recall. Companies now have to issue such recalls voluntarily.

“We need better abilities and authorities to put in place these preventive controls and hold companies accountable,” Hamburg said.

Food safety advocates have pushed for such improvements for more than a decade, as there have been few rules on the books that require companies to make eggs, along with many other foods, safer. The FDA’s authority on the farm is questionable as the agency is often limited to gathering information about a contamination outbreak after people have already been sickened. Investigations into what went wrong come well after the crucial evidence is gone.

FDA’s Farrar says the agency has traditionally focused on food manufacturing facilities instead of farms as the agency’s authority is muddled and there are few standards in place.

“The farm is just a different environment,” he said. “Without those standards we don’t have the specific information to say you are in compliance in this area and out of compliance here.”

The Obama administration has tried to remedy that with new rules that went into effect in July, just after the current egg outbreak began. The rules, which require producers to do more testing for salmonella and take other precautions, had languished for more than a decade after President Bill Clinton first proposed that egg standards be toughened. The FDA said in July that the new safeguards could reduce the number of salmonella cases by nearly 60 percent.

Those rules would be bolstered by the legislation, which the House passed more than a year ago but the Senate has not yet taken up. The bill would provide more money to the FDA for inspections and enforcement.

DeLauro said Monday that the absence of oversight and confusion surrounding egg inspections — the FDA inspects shell eggs while USDA inspects processed eggs — could eventually cost lives. She advocated a single food safety agency instead of the current system in which at least 15 agencies have a hand in ensuring the nation’s food is safe.

“You’ve got a company that has a pattern of regulatory noncompliance that should have sent a warning to federal regulators and warranted additional scrutiny,” she said. “If we were doing our job we would have a single food safety agency.”

The lack of oversight has become a bigger problem as the egg industry, like many other food industries, has consolidated over recent years, placing fewer, larger businesses in control of much of the nation’s egg supply to consumers.

Wright County Egg and Hillandale Farms share suppliers of chickens and feed as well as ties to an Iowa business with a long history of violating state and federal health, safety, immigration and environmental laws. FDA officials said last week they had “no inspectional history” with Wright County Egg.

Jewanna Porter, a spokeswoman for the egg industry, said the company Quality Egg supplies young chickens and feed to both Wright County Egg and Hillandale Farms. The two share other suppliers, she said, but she did not name them.

Businessman Austin “Jack” DeCoster, who has paid millions of dollars in fines for various violations to the government over the last 20 years, owns Wright County Egg and Quality Egg. Wright County Egg recalled 380 million eggs Aug. 13 after it was linked to the almost 1,300 cases of salmonella poisoning. A week later, Hillandale Farms recalled 170 million eggs.

“These are high-risk facilities so you need FDA checking on them regularly, at least once a year, to make sure they are complying with the regulations,” said Caroline Smith DeWaal, food safety director for the Center for Science in the Public Interest. “You can’t produce food at that level without a food safety cop on the beat.”

Lawsuits are building up against the companies. William D. Marler, a Seattle attorney for a person who filed suit alleging illness from tainted eggs in a salad at a restaurant in Kenosha, Wis., said his firm has been retained by two dozen families and was representing a woman who was hospitalized in California.

As for consumers, Hamburg had some practical advice: Reject over-easy eggs. Consumers should strictly avoid “runny egg yolks for mopping up with toast,” she said, and noted that it is impossible to see, smell or taste any difference between eggs tainted with salmonella and those that are safe.

The most common symptoms of salmonella poisoning are diarrhea, abdominal cramps and fever eight to 72 hours of eating a contaminated product.

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Online:

Food and Drug Administration: http://tinyurl.com/25ot6ss

Centers for Disease Control: http://tinyurl.com/27lla8y

Foodsafety.gov: http://www.foodsafety.gov

Egg Safety Center recall information: http://www.eggsafety.org