That's because illnesses occurring after mid-July may not be reported yet, said Dr. Christopher Braden, an epidemiologist with the federal Centers for Disease Control.
Almost 2,000 illnesses from the strain of salmonella linked to the eggs were reported between May and July, about 1,300 more than usual, he added. No deaths have been reported. The CDC is continuing to receive information from state health departments as people report their illnesses.
"I would anticipate that we will be seeing more illnesses reported likely as a result of this outbreak," said Braden. The recall of 380 million eggs from Iowa's Wright County Egg is one of the largest shell egg recalls in recent history.
The outbreak could have been prevented if new rules to ensure egg safety had been in place a few months earlier, an FDA spokeswoman said.
The rules, which require producers to do more testing for salmonella and take other precautions, went into effect in July. The FDA said at the time that could reduce the number of salmonella cases by nearly 60 percent.
"There are measures that would have been in place that could have prevented this," said Sherri McGarry of the FDA's Center for Food Safety and Applied Nutrition.
She and other officials declined to say what specific measures would have prevented this particular outbreak, citing an ongoing FDA investigation.
McGarry said illnesses were traced back to eggs produced on three of five farms the Iowa company owns. The investigation, which includes sampling, records review and sanitation assessments, is focusing on those three farms.
Salmonella is the most common form of food poisoning from bacteria, and the strain involved in the outbreak is the most common kind of salmonella -- accounting for roughly 20 percent of all such food poisonings.
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. 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.
Other states have seen a jump in reports of the same type of salmonella. Spikes or clusters of suspicious cases have also been reported in Arizona, Illinois, Nevada, North Carolina, Texas and Wisconsin.
The CDC said investigations by 10 states since April have identified 25 cases in restaurants where more than one person became ill. Preliminary information showed that Wright was the supplier in at least 15 of those.
Much of the investigation so far has been centered on restaurants in California, Colorado, Minnesota and North Carolina. They're not necessarily breakfast places -- it's possible some people got sick from eating salad dressing made with raw eggs, or eating soup with an undercooked egg dropped in, Braden said.
In North Carolina, a cluster of about 80 illnesses in April were linked to meringue-containing chocolate pie and banana pudding served at a Durham barbecue restaurant, health officials said.
Eggs from Wright County Egg were linked to illnesses in the four 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 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.
The form of salmonella tied to the outbreak 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.