An expert of U.S. Center for Disease Control (CDC) and Prevention (CDC) said Tuesday that the Cronobacter infections, which killed a 10-day baby in Missouri, could also be caused by environmental factors. Barbara Reynolds, an expert with CDC, said in an interview with Xinhua that U.S. government agencies are still performing tests to determine how infants contracted this rare bacterial infections, and the full test results would still \"take some time.\" The death of the Missouri infant attracted nationwide attention last week when it was questioned if the newborn\'s deadly Cronobacter infection could have been caused by Mead Johoson\'s Enfamil Premium Newborn powdered formula. A second case of the Cronobacter infection in an Illinois baby led retailers such as Walmart to pull the suspected Enfamil off its shelves, and prompted an investigation by U.S. federal agencies. It was a very rare disease with an average of only four to six cases a year in the United States, said Reynolds, adding that though the CDC has had concerns about infant powdered formula in past cases of Cronobacter infections, it currently remains to be seen whether the formula played a role in the recent cases. \"We have no test results yet that show contamination of the infant formula -- it\'s still being collected, it\'s still being tested,\" said Reynolds, adding that the CDC also had yet to find a connection between the two infants. The U.S. Food and Drug Administration (FDA) is also conducting ongoing tests on the Enfamil infant powder to determine if a batch was somehow contaminated with the bacteria. Mead Johnson, the company who produces the Enfamil brand, said in a statement Sunday that their own tests on the infant formula had not detected the presence of Cronobacter bacteria, and that Enfamil was safe for consumers.