Section 54. The department shall, when deemed necessary, but not more than once in each year, order an audit of the medical records required to be kept by a hospital, institution for unwed mothers out-of-hospital dialysis units or a clinic under the provisions of section fifty-three. Such audit shall be made by persons designated by the department, shall be conducted under the direction of the department and be made entirely at the expense of such hospital, institution for unwed mothers out-of-hospital dialysis units or clinic, as the case may be.