The U.S. Food and Drug Administration is stepping up tests on papayas imported from Mexico as it investigates a Salmonella outbreak in 23 states involving 97 cases of food poisoning, including 10 that required hospital treatment.

In a news release Monday, the FDA said 10 more papaya samples from Mexico have tested positive for different strains of Salmonella, in addition to two positive samples of the outbreak strain, Salmonella Agona, reported earlier — one in a shipment halted at the border and another collected at a Texas processing plant.

“As part of this investigation, the FDA is taking regulatory action to prevent potentially contaminated papaya from entering the United States, including increasing its sampling of imported papaya,” the agency stated.

The FDA said it is working with the importer, Agromod Produce of McAllen, TX, and state public health authorities to determine if previous shipments of potentially contaminated papaya could be in circulation. Agromod announced over the weekend that it was recalling papaya distributed before July 23 under four brand names — Blondie, Yaya, Ma√±anita, and Tastylicious.

Agromod distributed fresh, whole papayas, but retailers and others who received them could have further processed them, the FDA noted. The agency warned consumers not to eat papayas distributed by Agromod and to throw them away in sealed containers. It also said consumers should check with retailers to see if any papayas available for purchase may originally have come from Agromod. 

The company said it had shipped papayas to wholesalers and retail stores throughout the United States and Canada. Walmart said Monday that it had received some of the Agromod papayas.

Consumers with questions about the recalled papayas should call Agromod Produce, Inc. at 800-385-7658.

Meanwhile, the Centers for Disease Control and Prevention, in a report on the multistate outbreak, said 25 people have been identified as infected with the outbreak strain of Salmonella in Texas, as well as 17 in Illinois; eight in Georgia; seven in California; six in New York; five in Washington; three in Arizona, Minnesota, Missouri and New Mexico; two in Louisiana, Nebraska, Virginia and Wisconsin; as well as single cases in Arkansas, Colorado, Massachusetts, Nevada, New Jersey, Ohio, Oklahoma, Pennsylvania and Tennessee.

Most of the illnesses began on or after Jan. 17, 2011, the CDC reported, and those individuals range in age from less than one year to 91 years old. The median age is 20, and 41 percent are patients younger than 5. Sixty-three percent are female. Ten patients have been hospitalized. 

“Epidemiologic, laboratory and traceback information identifies papayas from Mexico imported through Agromod Produce Inc. as the likely source of infection,” the CDC wrote.

The FDA said it is working with Agromod and Mexican officials to determine how the papayas may have become contaminated.

Salmonella and norovirus are the primary bacterial and viral pathogens associated with consuming tropical fruits. In 2006, 26 cases of Salmonella Litchfield infection linked to papayas were reported in Australia. In 2009, there were 11 cases of Salmonella Saintpaul in another outbreak in Australia related to pawpaw, a papaya-like fruit.

Last year at least nine people in California and Nevada became ill with typhoid fever infections after eating Salmonella Typhi-contaminated frozen pulp from mamey, another tropical fruit.