The US health authorities think the bacteria is in tomatoes, chilli peppers and the coriander.
The outbreak is deemed to be the worst food-borne illness in the US for decades.
Investigators say they think there are several sources for the outbreak as many of those ill say they did not eat hot peppers or foods like salsa that contain them.
The US Food and Drug Administration (FDA) has warned against eating raw plum, round or Roma red tomatoes unless they are from certain states or abroad.
Cherry and grape tomatoes and those sold with the vine still attached have not been associated with the outbreak.
Home-grown tomatoes are also safe to eat raw, US officials say.
Symptoms of salmonella, which usually appear within 12 to 72 hours of eating contaminated food, include diarrhoea, nausea and vomiting, headaches, stomach cramps and fever.
The symptoms of salmonella can last for several days, but most people make a full recovery within a week.
Those most at risk of developing severe illness are the elderly, infants and people with weakened immune systems.