A few months back, I read about a potential source of CC that I'd never even thought of: pharmacists don't clean the trays between refills unless you specifically ask them to. So for the past few months, I've been asking them to clean the trays before filling my prescriptions to prevent CC. It turns out this might not be enough....
I'm currently taking Nystatin, which are dark red pills. This last time when I went to get my refill, the pharmacist said the pills already had white powder all over them and offered to order a new, unopened bottle for me. Turns out, even if you ask them to clean the tray between refills, it may be too late, because they may have previously poured the pills out onto the tray to fill someone else's prescription and not cleaned the tray during THAT refill and then returned the excess pills back into the bottle. The pharmacist recommended that if I'm really concerned about CC, to always get my prescriptions filled from unopened bottles.
I thought this info might help others, especially those that are more sensitive. I'm not sure if this applies to Costco or all pharmacies in general.