In my youth before going for national service, I used to work part time at a small factory business that fabricates and installs refrigeration systems - big huge refrigerator for cold storage that are massive rooms that can you can walk in and out of. This was a family enterprise and they did things the old ways by hand fabricating everything they needed with strong emphasis on workmanship, fabricating the wall panels, the chemicals contained in it for insulation, hand spray painting them, hand assembling compressors for the air conditioning even provisioning for the electrical wiring it was really really tough physical heavy labor with a lots of grease and grime in between. But I guess at that time it was better than idling away waiting to go NS.
Some the interesting clients that we install for are food factories producing birds nest, processed sharkfins, pork bak kua, beef ball/fishball, frozen fish, fruits and vegetables. After work when the employees go home you can usually see huge rats scurrying about scare the hell out of me
I can say almost all food companies are plagued with this kinds of hygiene issues. Anything that is cooked, left in the open will attract pests and impossible to eradicate because nobody can remember to clean up 100% there will always be 1 or 2 clever pests that manage to get thru. But sometimes could also be deliberate or sabotage.