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, or the equivalent of 19 million dozen-egg cartons, were recalled by the company Wright County Egg of Galt, Iowa. That number was increased to nearly 32 million dozen-egg cartons.
Salmonella is the most common bacterial form of food poisoning. The strain involved in the outbreak is the most common strain of salmonella, accounting for roughly 20 percent of all salmonella food poisonings.
The Food and Drug Administration also is investigating.
The initial recall was issued last week. Eggs affected by the expanded recall were distributed to food wholesalers, distribution centers 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," Wright County Egg officials said in a statement Wednesday evening.
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.
Thoroughly cooking eggs can kill the bacteria, but health officials are recommending people throw away or return the recalled eggs.