common vehicle transmission Transmission of a disease agent (infectious pathogen, toxic chemical, etc.) from a source that is common to those who acquire the disease. Common vehicles include air, water, food, injected substances. Legionellosis is an example of common vehicle spread in air that has passed through air conditioning equipment contaminated by the causal organism. HIV disease and hepatitis B and C can be spread among illicit drug users by the common vehicle of contaminated needles and syringes. Cholera and many other waterborne diseases are spread by the common vehicle of contaminated water. indirect transmission