Federal public health authorities estimate that up to 4 million cases of salmonellosis occur each year in the United States. Salmonella can cause what is known as a food-borne illness. That means it is caused by eating a contaminated food or beverage. Pathogens such as bacteria, parasites and viruses can cause food- borne sickness, as can any poisonous chemicals added to food. More than 250 types of food-borne diseases have been identified, according to the CDC, although people have also contracted illness from salmonella by handling animals that carry the bacteria.

At least 24 cases of salmonellosis have been reported so far this year in the Roanoke and Alleghany Health Districts, epidemiologist Lex Gibson said. The number of reported cases in the districts for all of 2004 was 46, which most were independent, unrelated cases, but several members of one family did get salmonella infections from eating eggs from their chickens.

The CDC estimates that 76 million cases of food-borne illness occur each year. Most are mild, but about 325,000 result in hospitalizations and 5,000 in death. And authorities believe many more cases are never reported at all. Though food-borne illnesses are generally treatable, public health officials are concerned because they are seeing more antibiotic-resistant pathogens. And they have also seen established pathogens turn up in new organisms.

Salmonella, for example, was always associated with eggs and chickens. But in recent years, public health officials have identified more strains of the bacteria in produce, and bacteria are also good at picking up genetic material and mutating, according to Dr. Robert Tauxe, chief of the Foodborne and Diarrheal Diseases Branch at the CDC.

Gibson said epidemiologists are seeing a rise in the number of a certain strain of salmonella, called salmonella enteritidis. This strain is more closely associated with poultry and is believed to be passed from hen to egg. "We’re seeing it all across the state," Gibson said. He estimated that 40 percent of the Virginia cases of salmonella are this particular strain, which can be carried inside an egg yolk.

According to Tauxe, during the 1970s, less than 1 percent of food-borne illnesses were associated with fresh produce, however through the 1990s, it rose to 6 percent. In recent years, food-borne illnesses in the United States have been traced to green onions and canteloupe from Mexico, snow peas from Guatemala and alfalfa from Australia, he said. The United States, in turn, has exported almonds with salmonella to Canada and ground beef with E. coli to Japan, he said.