The yeast in your product may not be caused from employees. It could be from other sources.
Yeast can survive under very harsh environments.
http://foodsafety.me...yeast-and-mold/
https://aggie-hortic...iology-of-food/
Yeasts and Molds
Yeasts and molds grow on most foods, on equipment, and building surfaces where there are small amounts of nutrient and moisture. Since bacteria grow faster, they greatly outnumber yeasts and molds in most foods. However, bacteria find conditions of low pH, moisture, or temperature and high salt or sugar unfavorable. In such environments, yeasts or molds predominate. Thus, they can be a problem in dry foods, salted fish, bread, pickles, fruits, jams, jellies, and similar commodities.