Maybe I didn't explain myself well regarding the pen delivery system.
The needle is a cap, which puntures a membrane in the cartridge of insulin (which contains more than one dose), and delivers the insulin directly from the cartridge subcuteously. You then pull it out of the skin, and remove the needle. the plunger that measures the dose is at the other end of the cartridge, and works on a pressure/suction basis.
Even if you dispose of the pen needle, the way the cartridge works could very easily suck in contamination. There are warnings about contamination in with the cartridges. It should NEVER be used for more than one person.
One would have thought, even without training, those in the healthcare field would have figured that out.