WASHINGTON (AP) — Food and Drug Administration investigators have found rodents, seeping manure, and maggots at the Iowa egg farms believed to be responsible for as many as 1,500 cases of salmonella poisoning.

FDA officials released their initial observations of the investigations at Wright County Egg and Hillandale Farms Monday.

The two farms recalled more than half a billion eggs after salmonella illnesses were linked to their products earlier this month.

The reports released by the FDA show many possible sources of contamination at both farms, including rodent, bug, and wild bird infestation, uncontained manure, holes in walls, and other problems.

Positive samples of salmonella linked to the outbreak have been found at both farms.

Officials said they still cannot speculate on how the eggs were contaminated. But they said the farms not only violated their own standards but also new egg rules put in place this summer.

Among the observations of the investigators:

• Live rodents in laying houses at both farms.
• Structural damage and holes in many locations at both farms, allowing wildlife access.
• Escaped chickens tracking manure through the houses.
• Employees not changing clothing properly when moving from one location to another and not sanitizing equipment properly.
• Live flies too numerous to count on egg belts, in the feed, and on the eggs themselves at Wright County Egg.
• Dead and live maggots “too numerous to count” on the manure pit floor in one location at Wright County Egg.
• Manure piled four to eight feet high in five locations at Wright County Egg, leaning against and pushing open doors that allowed wildlife to enter the laying houses.
• Nonchicken feathers in a laying house and wild birds flying in and out of two facilities at Wright County Egg.
• Manure seeping through the foundation to the outside of laying houses in 13 locations at Wright County Egg.
• Rusted holes in feed bins and birds flying over the feed bins at Wright County Egg.

Unidentified officials of Wright County Egg said they are working “around the clock” to address the FDA’s concerns and some already have been fixed.

Hillandale Farms released a similar statement, saying some of the issues already had been identified by the company.

Animal feces and access to wildlife are normally the main concern of investigators looking for causes of an outbreak, as illnesses such as salmonella originate from feces.

Michael Taylor, the FDA’s deputy commissioner for foods, said the agency cannot say how these conditions compare to other egg farms around the country but he believes they are “significant deviations from what is expected.”

The agency has not traditionally inspected egg farms until there has been a problem.

The FDA has said it had not inspected the two Iowa farms, even though the owners of Wright County Egg have a long history of health, safety, environmental, and immigration violations.

The FDA is planning to inspect all of the country’s largest egg farms before the end of next year.

An Obama administration official said inspectors will visit about 600 large egg farms that produce 80 percent of the nation’s eggs. This will be the first government effort to inspect large egg farms, as most of them have gone largely uninspected for decades.

The FDA’s plan for heightened inspections came after more than half a billion eggs linked to cases of salmonella poisoning were recalled from two Iowa farms this month. The inspections will be conducted as part of new FDA rules put in place this July to prevent salmonella in shell eggs.

The inspections will begin in September with the farms deemed highest risk to consumer safety, the official said. The new inspection plan covers all egg farms that have 50,000 or more hens.