One family of superbugs, known as carbapenem-resistant Enterobacteriaceae or CRE, may be spreading more widely than previously thought, according to a study published Monday in the journal Proceedings of the National Academy of Sciences. In fact, transmission of these bacteria person-to-person may be occurring without symptoms, say the researchers, from the Harvard T.H. Chan School of Public Health and the Broad Institute.CRE, which tend to spread in hospitals and long-term care facilities, cause an estimated 9,300 infections and 600 deaths each year in the United States, according to the Centers for Disease Control and Prevention.