No person shall be admitted into the county care facility as a resident except upon order of the board of supervisors, which shall be issued only after the person seeking admission has received a preadmission physical examination by a physician or physician assistant. However, if the need for admission of the person to the county care facility is immediate and no physician or physician assistant is readily available to perform the examination, the board may order the person’s admission pending an examination by a physician or physician assistant, any provisions of sections 135C.3 and 135C.4 to the contrary notwithstanding. When an admission is so ordered, the physical examination shall be completed within three days after the person’s admission to the county care facility.