Final answer:
A systemic infection occurs when pathogens spread throughout the entire body, rather than remaining localized to one area. It can affect multiple body systems and often follows a primary infection or occurs when treatment for an infection compromises the body's normal defenses.
Step-by-step explanation:
A systemic infection is when the pathogen has distributed throughout the body rather than staying in one area or organ. Infections can be local, staying in one small area like a boil caused by Staphylococcus aureus, or they can be focal, which is a small region of infection that can spread to another area. A systemic infection, however, affects the entire body. Examples of this include the varicella-zoster virus, which leads to the widespread skin lesions seen in chickenpox. These types of infections can become severe and may follow a primary infection that weakens the host's defenses, making them susceptible to other pathogens.
It is important to understand how infections can progress from local areas to a systemic spread. Pathogens enter the body through portals of entry and subsequent adhesion, invasion, and multiplication lead to an infection, which can remain localized or turn systemic if it disseminates. Secondary infections can arise due to a compromised immune system from a primary infection or as a result of antibiotic treatment affecting the normal microbiota. Awareness and prevention of systemic infections are crucial, as they pose a more significant health threat due to their ability to affect multiple body systems.