ATLANTA — Hundreds of people have been sickened in a salmonella outbreak linked to eggs in three U.S. states and possibly more, and health officials on Wednesday dramatically expanded a recall to 380 million eggs.

The Centers for Disease Control and Prevention is working with state health departments to investigate the illnesses. No deaths have been reported, said Dr. Christopher Braden, a CDC epidemiologist involved in the investigation.

Initially, 228 million eggs were recalled but that number was increased to the equivalent of nearly 32 million dozen-egg cartons.

Minnesota, a state with some of the best food-borne illness investigators in the country, has tied at least seven salmonella illnesses to the eggs.

Other states have seen a jump in reports of the type of salmonella. For example, California has reported 266 illnesses since June and believes many are related to the eggs. Colorado saw 28 cases in June and July, about four times the usual number. Spikes or clusters of suspicious cases have also been reported in Arizona, Nevada, Illinois, Texas and Wisconsin.

Salmonella is the most common bacterial form of food poisoning. And the strain involved in the outbreak is the most common strain of salmonella, accounting for roughly 20 per cent of all salmonella food poisonings.

Unfortunately, current lab tests do not allow health officials to fingerprint this form of salmonella as precisely as other kinds of food-borne illness. So determining the size of a salmonella enteritidis outbreak is a little more challenging, Braden said.

The Food and Drug Administration also is investigating.

Much of the investigation so far has been centred on restaurants in California, Colorado and Minnesota where sick people ate. They are not necessarily breakfast places -- it's possible some got sick from eating a salad dressing that had a raw egg in it, or eating soup with an undercooked egg dropped in, Braden said.

In one state, a cluster of illnesses seem to stem from meringue pie, health officials said.

Eggs from Wright County Egg in Galt, Iowa, were linked to several illnesses in the three states. The eggs were distributed around the country and packaged under the names Lucerne, Albertson, Mountain Dairy, Ralph's, Boomsma's, Sunshine, Hillandale, Trafficanda, Farm Fresh, Shoreland, Lund, Dutch Farms and Kemp.

The initial recall was issued last week. Eggs affected by the expanded recall were distributed to food wholesalers, distribution centres and food service companies in California, Colorado, Minnesota, Arkansas, Arizona, Georgia, Illinois, Iowa, Oklahoma, Oregon, Missouri, Nebraska, Nevada, Texas, Utah, Washington and Wisconsin.

"We are undertaking this additional recall to further protect the safety of consumers -- this voluntary measure is consistent with our commitment to egg safety, and it is our responsibility," Wright County Egg officials said in a statement Wednesday evening.

In an earlier statement, company officials said the FDA is "on-site to review records and inspect our barns." The officials said they began the recall Aug. 13.

The most common symptoms of salmonella are diarrhea, abdominal cramps and fever within eight hours to 72 hours of eating a contaminated product. It can be life-threatening, especially to those with weakened immune systems.

This form of salmonella can be passed from chickens that appear healthy. And it grows inside eggs, not just on the shell, Braden noted.

Thoroughly cooking eggs can kill the bacteria. But health officials are recommending people throw away or return the recalled eggs.