Appendix A: How Infections Spread

Germs are a part of everyday life and are found in our air, soil, water, and in and on our bodies. Some germs are helpful, while others are harmful. Many germs live in and on our bodies without causing harm, and some even help us to stay healthy. Only a small portion of germs are known to cause infection.

An infection occurs when germs enter the body, increase in number, and cause a reaction of the body.

Three things are necessary for an infection to occur:

• Source: Places where infectious agents (germs) live (e.g., sinks, surfaces, human skin). Germs are found in many places. People are one source of germs. People can pass germs to others, even if they do not have symptoms of an infection. Germs are also found in the school environment. Examples of environmental sources of germs include desks, lunch tables, faucets and sinks, and play items or shared instructional materials.
• Susceptible Person: A susceptible person is someone who is not immune or who has a weakened immune system. For an infection to occur, germs must enter a susceptible person’s body, invade tissues, and multiply.
• Transmission refers to the way germs infect a susceptible person. Germs depend on people, animals (e.g., mosquitoes), the environment, and/or shared objects to move. Some examples of ways that germs travel in school settings include contact (e.g., touching), sprays and splashes from coughs or sneezes, inhalation, insects, and through food or liquids (e.g., sharing with a sick person).
  • Contact occurs when a healthy person comes into direct contact with (touches) germs from a sick person. For example, if a child’s hands become contaminated by touching germs present on a desk, that child can then carry the germs on their hands and spread them to themselves or to a susceptible person when proper handwashing is not performed.
  • Sprays and splashes occur when an infected person coughs, sneezes, or vomits, creating droplets which carry germs short distances (within approximately 6 feet). These germs can land on a susceptible person’s eyes, nose, or mouth and can cause an infection. These sprays and splashes can also land on surfaces and contribute to contact transmission (as described above).
  • Inhalation occurs when germs are aerosolized in tiny particles that may be transmitted through air over greater distances and for a longer time. These germs may eventually be inhaled. How far a germ may spread depends on many factors including the type of germ and the ventilation of the area.
  • Vectors are living organisms that can carry and transmit an infectious pathogen. Vectors are insects such as mosquitoes, ticks, and fleas that can spread infections. A person who gets bitten by a vector and gets sick has a vector-borne disease such as lyme disease or West Nile virus disease.