CHICCO USA, INC. IS RECALLING APPROXIMATELY 18,000 BASES USED IN KEYFIT AND KEYFIT 30 REAR-FACING CHILD RESTRAINT SYSTEMS AND IN CORTINA TRAVEL SYSTEMS, AND STAND-ALONE BASES FOR THESE SYSTEMS PURCHASED SEPARATELY, THAT WERE MANUFACTURED BETWEEN FEBRUARY 26 AND MARCH 17, 2008. SOME OF THESE BASES HAVE A DEFECT THAT CAN PREVENT THE BASE FROM BEING TIGHTLY SECURED TO A VEHICLE WHEN THE LOWER LATCH ATTACHMENTS ARE USED AS A METHOD OF INSTALLATION. SPECIFICALLY, WHEN A DEFECTIVE BASE IS INSTALLED WITH THE LOWER LATCH ATTACHMENT STRAPS, THE WEBBING USED TO TIGHTEN THE BASE TO THE VEHICLE SEAT CAN SLIP THROUGH THE ADJUSTMENT LOCK.