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.
Eggs from Wright County Egg in Galt, Iowa, were linked to several illnesses in three states.
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 percent of all salmonella food poisonings.
Thoroughly cooking eggs can kill the bacteria. But health officials are recommending people throw away or return the recalled eggs.