There are a number of schemes for classifying disease transmission. The various classification schemes are similar, but have slight differences, because some disease may be transmitted by more than one mechanism. For this module the outline in the table below will be followed.

Person-to-person Spread

1. Direct person-to-person

  • Sexual transmission (STDs/STIs)
  • Perinatal mother to child transmission
  • Needle injection
  • Skin-to-skin
  • Human bites

2. Indirect person-to-person

  • Fomites (contaminated objects)
  • Air: Droplet nuclei (true airborne) & Droplets

Common Vehicle Spread

1. Ingested: food-borne & water-borne; fecal-oral

2. Biological products: vaccines, sera, blood products 


Zoonoses: from vertebrate animals

1. Animal bites (e.g., rabies virus or hepatitis from primates)

2. Blood-borne, airborne


Vector Borne: mosquitoes, flies, fleas, ticks

  Two key concepts to bear in mind:

  1. Many diseases can be transmitted by more than one mechanism.
  2. Some mechanisms of transmission might logically fit into more than one category. For example, fecal-oral transmission occurs most commonly via "common vehicle transmission," i.e., ingestion of infectious agents in contaminated food or water, but fecal-oral transmission can also occur directly during anal sexual contact