All persons who come in contact with grade A raw milk shall exercise scrupulous cleanliness and shall not be afflicted with any communicable disease or be in a condition to disseminate the germs of any communicable disease which is liable to be conveyed by milk. The absence of such germs in all such persons may at the discretion of an approved or established milk inspection service be determined by bacteriological and physical examination in such manner as may be prescribed by the director and by such person or laboratory which is approved in writing by the department, conducted at the time of employment and every six months thereafter in a manner which is approved by the director.