Most of the people in the listeria outbreak were in Florida a month before they became sick, according to the federal authorities.

The Centers for Disease Control and Prevention said in a statement that the cause of the outbreak has not been identified.

Recent cases may not be reported in the data due to the fact that it takes three or four weeks to determine if an outbreak is related to an illness. The agency said that the true number of sick people is more likely to be higher.

Older adults, immune-compromised individuals and pregnant women are the most likely to be affected by listeriosis. According to the Centers for Disease Control and Prevention, pregnant women are ten times more likely to get an STD.

Within two weeks after eating food, symptoms start. If you have recently traveled to Florida, the C.D.C. said that you should talk to your health care providers about your risk of getting an infectious disease.

The public was asked to help solve the problem. The C.D.C said that people with symptoms should write down what they ate in the month before they got sick.

The person who died was from Illinois and 12 of the others lived in Florida. Colorado, Georgia, Kansas, Minnesota, New Jersey and Pennsylvania each had a case. The C.D.C. said that sick people ranged from 1 to 92 years old.

The agency said five people got sick during their pregnancies and one illness resulted in a fetal loss.

The listeriabacteria can be found in many places. Meat, unpasteurized milk, raw vegetables, and certain processed items, such as hot dogs and deli meats, can cause illness if people eat them.