I don't know how nicotine would effect contamination.
"Ultrasonic humidifiers make a cool mist which includes impurities from the liquid, viruses and bacteria are not neutralised in the process."
"There is an illness called 'humidifier fever' - "It is a flu like illness marked by fever, headache, chills myalgia and malaise but without prominent pulmonary symptoms. It normally subsides within 24 hours without residual effects,and a physician is rarely consulted. Humidifier fever has been relate to exposure to amoebae, bacteria, and fungi found in humidifier reservoirs, air conditioners and aquaria."
HUMIDIFIER FEVER is a respiratory disease caused by an immune reaction to inhaling aerosols containing various organic materials
http://www.e-cigarette-forum.com/fo...esign-requests/2705-ultrasonic-atomisers.html
I am so glad you have broken your silence.

This, I think, lends to how important it is to either change your cartridges at least once a week or give them a good scrub.
Everyone make sure you clean your mouthpieces regularly if you aren't going to change them out! And if someone has a hoot off of your ecig... Clean it or get a new mouthpiece!