A focal infection occurs when a localized pathogen, or the toxins it produces, spread to a secondary location. For example, a dental hygienist nicking the gum with a sharp tool can lead to a local infection in the gum by *Streptococcus* bacteria of the normal oral microbiota. They may then gain access to the bloodstream,  resulting in a secondary infection.

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Infections can be described in 3 ways, depending on the extent of the infection:
- local
- focal
- systemic

Types of Infections 

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A local infection is confined to a small area of the body, typically near the portal of entry. An example is when hair follicle infected by *Staphylococcus aureus* infection may result in a boil around the site of infection.

Localized Infection

Focal Infection

If an infection becomes spread throughout the entire body, we call it a systemic infection. An example is the varicella-zoster virus which typically gains entry through a mucous membrane of the upper respiratory system. It then spreads through the body, resulting in the classic red skin lesions associated with chickenpox. Since these lesions are not sites of initial infection, they are signs of a **systemic infection**.

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