From the Wikipedia page 
The 1848 Act was replaced by the Local Government Act 1858 (21 & 22 Vict. c. 98). The act came into force in all existing local board of health districts on 1 September 1858. The act made some changes to the procedure for constituting a local board and gave them some additional powers. There was also a change in nomenclature: the authorities created by the 1858 act were simply entitled "Local Boards" and their areas as "Local Government Districts".