What is infection? Define and explain the chain of infection.

The chain of infection is a model that describes the sequence of events that must occur for an infection to spread from one person or place to another. Breaking any link in this chain can prevent the spread of disease.

Here are the six links in the chain of infection:

1. Infectious Agent: The pathogen (e.g., bacteria, virus, fungus, parasite) that causes the disease.
2. Reservoir: The natural habitat where the infectious agent lives and multiplies. This can be humans, animals, insects, soil, or water.
3. Portal of Exit: The path by which the infectious agent leaves the reservoir. Examples include respiratory secretions (coughing, sneezing), blood, feces, urine, or open wounds.
4. Mode of Transmission: The method by which the infectious agent travels from the portal of exit to a new host. This can be direct (e.g., touch, sexual contact, droplet spread) or indirect (e.g., airborne, vector-borne, vehicle-borne like contaminated food or water).
5. Portal of Entry: The path by which the infectious agent enters a new host. This can be similar to the portal of exit, such as the respiratory tract, gastrointestinal tract, broken skin, or mucous membranes.
6. Susceptible Host: An individual who lacks effective resistance to the infectious agent and is therefore vulnerable to infection. Factors like age, immune status, chronic diseases, and vaccination status can influence susceptibility.