It shall be unlawful to employ in any premises open to the public or engaged in the transportation, processing, preparation or packaging of food or beverages any person who the employer knows or should know, based upon reasonable observation, is afflicted with, or who is a carrier of, any contagious or infectious disease; and it shall be unlawful for any person who knows or should know that he or she is afflicted with or a carrier of any such disease, to work in or about any such premises.