Simply the fact that smokers bring their hands to their faces, often touching or coming close to touching their face, can also increase the likelihood of infection
Proctor (December 1996), "The anti-tobacco campaign of the Nazis: a little known aspect of public health in Germany, 193345", British Medical Journal , 313 (7070): 14501453, doi:10.1136/bmj.313.7070.1450, PMC 2352989, PMID 8973234 "Research on Smoking and Lung Cancer: A Landmark in the History of Chronic Disease Epidemiology"
Tahoe conservationists distribute new cigarette canisters STATELINE The oldest and largest conservation group at Lake Tahoe and a coalition of water suppliers plan to start distributing 250 cigarette butt collection canisters around the lake this summer to help protect the cobalt blue waters and reduce litter on the shoreline
G., Fabricant, J., Litrenta, M