(NBC) - Investigators are still looking for the source of salmonella contamination at Wright County Egg and Hillandale Farms in Iowa that sparked the largest egg recall in recent history.
FDA teams also plan to conduct hundreds of inspections of other egg producers to make sure they adhere to new safety rules implemented just after the initial salmonella outbreak.
Officials say if they had been in effect earlier, it could have prevented the recall.
The president of Sauder's Eggs welcomes the new regulations.
"These new rules are adapted and patterned after what we have been doing for the last 20 years and our company was a pioneer in developing these rules and we do know it works," said Paul Sauder. "I can tell you first hand that when we first started the program we had about 30 percent of our chicken houses were positive for salmonella and now we have less one half of one percent."
He says even though the majority of eggs produced are safe, the recall has impacted the entire industry.
"It is very difficult and nerve wrecking to have this incident happening for the rest of the industry and a for the consumers out there to understand how this can happen."
One issue under investigation is sanitation.
Iowa's top poultry veterinarian says mice could be a prime suspect.
"If a chicken consumes the feed with the mouse fecal pellets, the chicken becomes infected, and subsequently, the chicken will transmit this bacteria in its own droppings to other birds," explains Iowa State University's Dr. Darrell Trampel.
Infected hens can then transmit salmonella directly to their eggs.
The FDA says at this point it doesn't think any other farms are involved in the outbreak.
Inspectors in Iowa say they'll have more results by the end of the week.