California Code, Health and Safety Code - HSC § 101425

The board of supervisors or the governing body of any city may contract with the county superintendent of schools or with the governing board of any school district located wholly or partially in the county or city for the performance by local health officers or other public health department employees of any or all of the functions and duties set forth in Chapter 9 (commencing with Section 49400) of Part 27 of the Education Code, relating to the health supervision of school buildings and of pupils enrolled in the schools of any or all school districts over which the county superintendent of schools, or the governing board or a school district, has jurisdiction.

The contract may specify payment dates as agreed upon by the parties to the contract;  payment shall be made as specified in the contract to the county treasurer or city treasurer.