Q+A: What are the details of the U.S. egg recall?

WASHINGTON (Reuters) - Two Iowa egg farms have recalled more than half a billion eggs as part of the largest U.S. salmonella outbreaks in a decade that may have caused up to 2,000 illnesses across the country.

Below are some questions and answers about the recall and the outbreak:

WHAT EGGS ARE RECALLED?

Two large Iowa egg producers, Hillandale Farms of Iowa and Write County Egg, and several of their distributors announced voluntary recalls last week for eggs shipped .

Their eggs were sold under the following brand names: Hillandale Farms, Sunny Farms, Sunny Meadow, Wholesome Farms, West Creek, Lucerne, Albertson, Mountain Dairy, Ralph's, Boomsma's, Sunshine, Hillandale, Trafficanda, Farm Fresh, Shoreland, Lund, Dutch Farms, Kemps, James Farms, Glenview, Pacific Coast, Alta Dena Dairy, Driftwood Dairy, Hidden Villa Ranch, Challenge Dairy and Country Eggs.

To see the full listing of recalled plant codes found on cartons or case labels, go to r.reuters.com/nur66n.

HOW MANY EGGS HAVE BEEN RECALLED?

Wright County Egg has recalled 380 million eggs and Hillandale Farms recalled 170 million, bringing the total recall to 550 million eggs.

HOW WILL THE OUTBREAK AFFECT EGG CONSUMPTION?

Egg consumption may suffer from long-lasting effects of this outbreak. "It definitely takes some time for the consumer to start trusting that particular food item or that brand again" even after a recall is over, Morningstar analyst Michelle Chang said.

WHICH STATES ARE AFFECTED BY THE RECALL?

The recalled eggs were sold in 22 states: Arizona, Arkansas, California, Iowa, Illinois, Indiana, Kansas, Minnesota , Missouri, Nebraska, North Dakota, South Dakota, Ohio, Texas, Wisconsin, Nevada, Colorado, Oklahoma, Washington, Oregon, Georgia and Utah.

HOW MANY PEOPLE GOT SICK FROM THE OUTBREAK?

The CDC says 1,993 cases of salmonella have been reported since May 1. Only about 700 cases would normally have been reported during the same time, the CDC says -- although it estimates that 40,000 Americans get salmonella every year. Most cases are never reported.

WHY WERE EGGS RECALLED?

The eggs from Hillandale Farms and Wright County Eggs may have caused the outbreak of Salmonella enteritidis around the United States. Salmonella is a bacteria found on the surface of egg shells and inside raw eggs and can cause fever, diarrhea, vomiting, abdominal pain and sometimes more serious illness or death.

HOW DOES SALMONELLA INFECT EGGS?

Salmonella originates in intestinal tracts of chickens and may be transmitted from an infected hen to the egg. Chickens can get infected through tainted seed, bacteria-carrying rodents and lax safety practices at pullet-rearing or hatchery facilities. FDA said a hatchery that supplied chicks to Hillandale Farms and Wright County Eggs is salmonella-free and has eliminated it as a possible source.

WHEN WILL THE CAUSE OF THE OUTBREAK BE KNOWN?

FDA expects to publish its first findings at the end of the week, but the investigation may continue after that.

(Additional reporting by Emily Stephenson in Chicago; editing by Sofina Mirza-Reid)