Tomatoes and lettuce, which many of the people affected more commonly ate, are the early suspects believed to be responsible for hospitalizing eleven people with salmonella poisoning since the first reports of the illness on 1 September.
The latest outbreak follows a series of food poisoning cases that have made the headlines recently. In September also, spinach contaminated with E. coli bacteria killed three people and infected more than 200.
Researchers from the U.S. Centers for Disease Control and Prevention, in collaboration with state departments of health and the Food and Drug Administration (FDA), have been testing and interviewing victims to determine the exact source of the salmonella outbreak.
No link has yet been made to any retailer, restaurant or food firm.
Tomatoes are particularly susceptible to contamination as salmonella can form during flowering and grow inside as the fruit develops, rendering external washing useless.
PulseNet, the network of public health laboratories that performs DNA fingerprinting on bacteria that cause foodborne illnesses, two weeks ago identified the specific strain causing the illness as salmonella typhimurium.
This strain typically causes an illness with fever and diarrhea that commonly resolves after about one week, other symptoms can include symptoms can include, nausea, vomiting, abdominal cramps, and headache.
Risk of infection from the most recent outbreak is now considered small, the CDC has said, following few new cases being detected.
Dr. David Acheson, FDA chief medical officer, said the contaminated fresh food had likely now been either eaten or thrown away. The agency is not advising the public to avoid any types of food as a result.
There have been nine salmonella outbreaks involving tomatoes since 1990, while officials estimate there are 1.4m cases of salmonellosis, the illness caused by the bacteria, in the US every year.