Germs are everywhere, but not all germs cause disease. However, all disease is caused by germs and it’s important to understand how infection spreads in order to combat it. The spread of infection requires a source, a susceptible person, and a transmission.


The source of infection can be a microbe such as bacteria, viruses, fungi, and protozoa. Vectors of infection can be people or environmental sources such as dry surfaces; wet surfaces, moist environments, and biofilms; or dust, debris, and decay.

Susceptible Person

While anyone can contract an infection or illness (even people who have been vaccinated), it is true that some people are more susceptible than others. People with weakened immune systems are most vulnerable.

A person’s immune system can become temporarily or permanently compromised by:

  • Underlying medical conditions such as cancer, diabetes, and organ transplants
  • Openings such as surgical incisions and IV catheters
  • Medications such as chemotherapy, antibiotics, and steroids

People who happen to be vulnerable due to a weakened immune system should read up on the methods of transmission and make sure that they are not any more exposed than they have to be.


For an infection to occur, the source must be introduced to the susceptible person. There are several different ways that this can happen.

Germs can be transmitted through touch and personal contact. This is one reason why frequent handwashing and good hand hygiene is so important.

Germs can also be spread through sprays and splashes when an infected person sneezes, coughs, or spits. These droplets can travel up to six feet, and they can cause infection if they land on a susceptible person’s eyes, nose, or mouth.

Germs can spread through inhalation, which is when germs become aerosolized and are able to travel long distances to reach a susceptible person. Germs can become aerosolized when an infected person talks, coughs, or sneezes.

It is also possible to transmit germs through sharps injuries or other puncture wounds. This happens when a sharp object becomes contaminated with bloodborne pathogens such as HIV or hepatitis, and then punctures the skin of the susceptible person.