Tomatoes are back on grocers' shelves and on McDonald's hamburgers, but federal investigators still haven't identified the source of the salmonella outbreak tentatively linked to certain types of tomatoes and they concede that the outbreak may be continuing -- meaning consumers may still be getting sick.
In its latest report, the Centers for Disease Control and Prevention (CDC) raised the number of salmonella cases linked to raw tomatoes to 810 people in 36 states, making this biggest U.S. salmonella outbreak linked to fresh produce.
The actual number is likely much higher. The CDC estimates that for every case that is reported, there are 30 cases that go unreported.
Symptoms of salmonella include bloody diarrhea, abdominal pain and fever.
While CDC scientists say the link to tomatoes still appears "strong," investigators are looking at other culprits as well.
"We always keep an open mind," CDC official Patricia Griffin said.
Not only have investigators not pinpointed the source of the outbreak, they're not sure it's over.
The latest known salmonella victim became ill on June 15, more than two months after the first reported illness and weeks after the first warnings about tomoatoes were issued.
Investigators have looked at farms in Florida, Mexico and elsewhere and they've examined packing houses and other facilities but have so far come up empty-handed.
Officials caution that the source may never be found.
The task is made more difficult because many tomato fields are no longer in production. Also, tomatoes from various sources are routinely mixed together at packing houses and other transit points, making it nearly impossible to say for sure where a given tomato came from.
Tomatoes thought to be the riskiest include raw red Roma, raw red plum, raw red round tomatoes, or products that contain these types of raw red tomatoes.
