Understanding the Spread of Infection

• Any microorganism that is able to cause infection. This can be a bacterium, virus, parasite, fungus or prion.

• Any place that an infectious agent can live and reproduce. This can include people, contaminated food or water, insects, or animals.

• The way the infectious agent leaves the reservoir. This can occur through the mouth and nose (e.g., coughing or sneezing), gastrointestinal tract excretions (e.g., vomiting or diarrhea), blood, or drainage from wounds.

• The way the infectious agent travels. This can be through:
• Direct contact from one person to another (i.e., touching), or indirect contact (i.e., from one person to an object or surface and then to another person).
• Droplets when a person coughs or sneezes.
• The air (airborne) when extremely small particles are released from one person and then inhaled by another person.

• The way an infectious agent enters a susceptible host. The individual may breathe it in, touch their eyes, nose or mouth, or eat or drink contaminated food or water. The infectious agent may also enter through breaks in the skin.

• Any person who is at risk of developing an infection. The individual risk will depend on the infectious agent and personal factors such as age, immune system function, and vaccination history, among others.

• Breaking any link in the chain of transmission will stop the transmission of the infectious agent and stop the spread of infection.

Ways to stop the spread of infection include:

• Frequent hand washing
• Ensure vaccinations are up-to-date
• Stay home when you are sick
• Cover your coughs and sneezes
• Environmental cleaning and disinfection
• Proper food storage
• Water treatment
• Proper waste disposal
• Treatment with antimicrobials, when appropriate

• Ottawa Public Health. (2024). Chain of Infection. Retrieved from Ottawa Public Health website.
• Provincial Infectious Disease Advisory Committee (2012). Routine Practices and Additional Precautions in All Health Care Settings. Toronto, Canada: Queen's Printer for Ontario
• Public Health Ontario. (2020). IPAC Core Competencies - Risk Assessment and Chain of Transmission.