The number of Americans sickened by salmonella-contaminated tomatoes has soared to 756, making it the largest outbreak connected to the crop since the Centers for Disease Control and Prevention started keeping records in the 1960s.

The actual number of illnesses is likely much higher. For every laboratory-confirmed case, the CDC estimates that another 30 illnesses go unreported. That works out to more than 22,600 potential illnesses in the tomato outbreak.

In Georgia, 15 cases — all but one in metro Atlanta — have been linked to the outbreak. Three of those patients were hospitalized and released, said Cherie Drenzek, an epidemiologist for the state Division of Public Health. The state is awaiting lab results on a few other cases, Drenzek said.

The second-largest salmonella outbreak linked to tomatoes sickened 510 in 2002.

Many of the newly reported cases are not due to a large number of recent illnesses, the CDC said. Instead, state health laboratories are doing a better job of looking for and diagnosing salmonella infections.

Still, the CDC classifies the outbreak as continuing, with the most recent cases occurring June 13, a week after federal authorities warned against eating certain types of tomatoes. The most recent illness confirmed in Georgia started on June 11.

It can take two weeks or longer to link an infection to the salmonella saintpaul strain behind the outbreak. That confirmation starts with a person experiencing symptoms such as nausea and diarrhea, and seeking medical help. A doctor might order a stool sample sent for testing to a private lab to discover the source of the gastrointestinal illness.

If that lab turns up salmonella, an illness that must be reported to public health authorities, a state lab will conduct further testing. A method called pulsed-field gel electrophoresis compares the strain of salmonella from a patient with the outbreak serotype. If they match, it's a confirmed case.

The majority of infections have occurred in Texas, with 330 cases, and New Mexico, with 80, the CDC said.

In Georgia, none of the cases appear to be related, Drenzek said. Epidemiologists have interviewed 10 of those sickened. They reported eating tomatoes bought in supermarkets or in restaurants. Many ate the tomatoes in pico de gallo, salsa or guacamole, she said.

The U.S. Food and Drug Administration sent investigators to farms in Florida and Mexico last week to examine steps along the distribution chain — from farms to packinghouses and distribution centers — to try to discover the source of the outbreak.

The FDA advises that grape tomatoes, cherry tomatoes and those sold on the vine are safe to eat. Round red tomatoes, Roma and plum tomatoes from areas cleared by the FDA are also safe to eat. For a list of approved growing regions, which includes Georgia, North Florida and other Southeastern states, go to www.fda.gov.

The FDA plans an update on the investigation Friday.