The salmonella-contaminated tomatoes have sickened more than 270 people, but investigators still continue the work to confirm the source of the outbreak, which remained elusive. At least 43 people have been hospitalized since mid-April and May, when authorities found cases of salmonella infections in Arizona, Colorado, Idaho, Illinois, Indiana, Kansas and Utah.

The salmonella outbreak has expanded to five more states and the District of Columbia, according to the Centers for Disease Control and Prevention.

US food safety officials on Monday said they hope that the cluster of nine people who became sick after eating tomatoes from the same company yields clues that lead them to the source of the outbreak that has sicken 277 people in 28 states.

“It's essentially a very solid lead for us,” David Acheson, director of food safety for the U.S. Food and Drug Administration, said in a press meeting, adding that the cluster is confined to a single geographic location and that all the sickened individuals appeared to have eaten similar types of tomatoes, Reuters reported.

Since mid-April, at least 43 people have been hospitalized with Salmonella Saintpaul, an uncommon form of the bacteria. No deaths have officially been attributed to the outbreak.

According to Centers for Disease Control, most people infected develop diarrhea, fever and abdominal cramps within 12 to 72 hours, the illness lasts four to seven days and in case of a severe infection, salmonella may spread from the intestines to the bloodstream and to other body sites and can cause death.  

The states affected include: Arizona, California, Colorado, Connecticut, Florida, Georgia, Idaho, Illinois, Indiana, Kansas, Michigan, Missouri, New Mexico, New York, Oklahoma, Oregon, Tennessee, Texas, Utah, Virginia, Vermont, Washington and Wisconsin.