Any county or two or more adjacent counties may, by resolution of the county board or county boards of the respective counties, as the case may be, or upon approval by referendum as hereinafter provided, establish and maintain a full-time health department; provided, that four or more counties must obtain the approval of the State Department of Public Health prior to establishing a multiple-county health department. The approval may be obtained upon application by the county board of any county, containing such information as may be required by the State Department. Approval shall be granted if the State Department determines that the establishment of the multiple-county health department is essential to the health requirements of the area affected.
     A “consolidated health department” shall mean a health department which has resulted from the merging of two or more adjacent existing county or multiple-county health departments, as provided in Section 5-25019.
     A full-time health department is one whose personnel, other than consultants and clinicians, devote their full time during regular, standard working hours to health department duties. Reference hereinafter made to health departments means full-time health departments unless otherwise specified.