(CNN) -- The number of cases of sickness caused by tomatoes has risen in recent days; 383 people have been infected with a rare form of salmonella since April in 30 states and the District of Columbia, federal health officials said Wednesday.
At least 48 people have been hospitalized in connection with a salmonella outbreak in tomatoes.
At least 48 of the victims, who range in age from younger than 1 to 88, have been hospitalized, an official with the Centers for Disease Control and Prevention said.
No deaths have officially been blamed on the outbreak, but the infection may have contributed to the death in Texas of a man in his 60s who also had cancer, the CDC said.
The increase reported Wednesday resulted not from a large number of new cases but from improved surveillance by state health departments in response to the outbreak and from the fact that laboratories completed analyzing samples, said Dr. David Acheson, associate commissioner for foods at the Food and Drug Administration.
Still, the outbreak is considered ongoing, with onset of illness in the latest case June 5.
"We do not think the outbreak is over," said Dr. Robert Tauxe, deputy director of the Division of Foodborne, Bacterial and Mycotic Diseases at the CDC.
All of the victims have been infected with a strain of Salmonella Saintpaul.
Acheson said that although there is a "high likelihood" that the contaminated fruit came from Florida or Mexico, authorities have not been able to pinpoint the source and may never be able to do so.
"We may not ultimately know the farm where these came from," he said. "Personally, I am still optimistic, but I'm trying to be realistic."
Acheson said Mexican health authorities have reported "some cases" of Salmonella Saintpaul, but he did not know whether they share the genetic fingerprint that marks the U.S. cases.
The FDA is testing tomatoes both domestically and as they cross the southern border, he said.
He said FDA plans to hire more inspectors to tighten scrutiny of food processing plants.
Tauxe said it is not possible to say whether the outbreak has peaked: "We really cannot predict what the final number is going to be or even what the shape of the curve is going to look like."
Cherry tomatoes, grape tomatoes and tomatoes with the vine still attached have been deemed safe, as have tomatoes from northern Florida, Acheson said. Roma plum and red round tomatoes are safe to eat if they are from areas that have been excluded, he said.
A list of such areas is posted on the FDA's Web site.