WASHINGTON » Food and Drug Administration investigators have found rodents, seeping manure and even 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 yesterday. 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 different possible sources of contamination at both farms, including rodent, bug and wild bird infestation; uncontained manure; holes in walls; and other problems that could have caused the outbreak. 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 and mice in laying houses at both farms

» Structural damage and holes in many locations at both farms, allowing wildlife access

» "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 4 to 8 feet high in five locations at Wright County Egg, leaning against and pushing open doors that allowed wildlife to enter the laying houses

» Manure seeping through the foundation to the outside of laying houses in 13 locations at Wright County Egg

In a statement, unidentified officials of Wright County Egg said they are working "around the clock" to address FDA’s concerns, and some have already been fixed.

"To date, the vast majority of the concerns identified in the FDA report already have been addressed through repairs or other corrective measures," the company said in the statement. "We anticipate the expeditious completion of nearly all remaining items by mid-September."

Hillandale Farms released a similar statement, saying some of the issues had already 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 in a briefing yesterday that the agency cannot say how these conditions compare with other egg farms around the country, but that 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 has not inspected either of 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 will now inspect all of the nation’s largest farms by the end of next year, the Obama administration announced last week.