(CNN) -- A fourth infant has been discovered to have been infected with a rare, sometimes fatal form of bacteria that can come from baby formula, but there is no evidence the cases are related, federal health authorities said Friday.
"Based on test results to date, there is no need for a recall of infant formula and parents may continue to use powdered infant formula, following the manufacturer's directions on the printed label," the Centers for Disease Control and Prevention and the Food and Drug Administration said in a joint update.
The latest case of Cronobacter infection occurred in Florida, the update said. After cases occurred in Missouri and Illinois, authorities looked for other cases, and found an Oklahoma case and the one in Florida. The Florida and Missouri infants died this month of their infections.
The Missouri case prompted retail giant Wal-Mart to pull all cans of the same size and lot number of baby formula from its shelves.
But DNA fingerprinting of the bacteria from the Missouri and Illinois cases found the bacteria differed, suggesting they were not related, the agencies said. Bacteria from the other two cases were not available for testing, they said.
In the Missouri case, Cronobacter bacteria were found in an opened bottle of nursery water and prepared infant formula, but it was not clear how they became contaminated, the update said.
Tests on factory-sealed containers of powdered infant formula and nursery water with the same lot numbers turned up no Cronobacter bacteria, it said, adding, "There is currently no evidence to conclude that the infant formula or nursery water was contaminated during manufacturing or shipping."
Formula maker Mead Johnson Nutrition said the agencies' test results corroborated its own. "We're pleased with the FDA and CDC testing, which should reassure consumers, health care professionals and retailers everywhere about the safety and quality of our products," Tim Brown, senior vice president and general manager for North America, said in a statement. "These tests also reinforce the rigor of our quality processes throughout our operations."
Cronobacter infection typically occurs during the first days or weeks of life. In a typical year, the CDC said, it learns of four to six such cases. This year, with increased awareness of the infection, it has tallied 12 cases.
The bacteria can cause severe infection or inflammation of the membranes that cover the brain. Symptoms can start with fever, poor feeding, crying or listlessness.
"Any young infant with these symptoms should be in the care of a physician," the update says.
The bacteria can be found in the environment and can multiply in powdered infant formula once it is mixed with water, said the CDC, which recommends breastfeeding whenever possible.
Cronobacter is fatal in nearly 40% of cases, according to the CDC. Infection survivors can be left with severe neurological problems.
CNN's Miriam Falco contributed to this report.