Oh ye, forgot to add. I've only seen once the "contaminated" tag on weed. Uber rare considering that I've accumulated over 19mln in one save xD

the achievement isn't broken, i obtained it by accident on my first playthrough but i'm not sure how to reproduce it.
edit: thinking about it.. did you try it with meth? if you don't use a detoxifier they might get sick because of the toxic gases. worth a try.

Originally posted by _Red_:

if you don't use a detoxifier they might get sick because of the toxic gases. worth a try.

I've tried it and it just kills the people that don't wear helmets, people that do wear them seems to be unaffected by that.

i think, they get sick ,when they can't use the shower

Easy way to get that achievement is set up small staff break room with arcade+tv+one sofa+coffee vender and snack vendor / one small kitchen room with 2 counters for cutting board and microwave, with fridge and table / staff washroom with toilet and hand dryer / bedroom with 3 beds. Notice I didn't add any like trash bin, shower, washroom sink. . . that will clean themselves. Don't put them in and set 3 staff's room to those rooms only and the rest are not allow for them to use. They will stay there till it get very dirty that will effect the contaminated into those vendors or fridge where they will ended up eat them to get them sick. Voila you got your achievement.

Hope it will help you that way.