(CNN) -- Fifteen people in four states have been infected with Listeria monocytogenes, linked to eating contaminated cantaloupes from the Rocky Ford region of Colorado, federal authorities said Tuesday.
The outbreak has infected 11 people in Colorado, two in Texas and one person each in Nebraska and Oklahoma, according to the Centers for Disease Control and Prevention.
Eating food tainted by the bacterium Listeria monocytogenes can cause listeriosis, an uncommon but potentially fatal infection, according to the Colorado Department of Public Health and Environment.
Those at high risk for listeriosis are pregnant women, people age 60 and older or those who have weakened immune systems from transplants, certain chronic diseases, or immunosuppressive therapies or medications, Colorado officials said.
"People at high risk for Listeria infection should not eat cantaloupe from the Rocky Ford growing region," said Dr. Chris Urbina, chief medical officer and executive director of the Colorado Department of Public Health and Environment. "The department expects additional test results later this week that may help identify the specific source of the cantaloupe linked to the multistate outbreak."
Healthy adults under age 60 rarely develop the illness, Colorado officials said.
Symptoms of the illness can include fever and muscle aches as well as diarrhea, headache, stiff neck, confusion and convulsions, Colorado officials said. The disease can also cause miscarriages and stillbirths, state officials said.
Antibiotics given promptly can cure the sickness and prevent infection of a fetus, Colorado officials said.
Even with prompt treatment, some Listeria infections result in death, particularly in older adults and in people with other serious medical problems, Colorado officials said.
The U.S. Food and Drug Administration is conducting investigations in the four states where illnesses occurred to determine the exact source of contamination, federal officials said.
Suspected cases are being investigated in several other states, the CDC said.
CNN's Michael Martinez contributed to this report.