Final answer:
Focal infections, such as those caused by Staphylococcus aureus or Mycobacterium tuberculosis (TB), typically start as local infections.
Step-by-step explanation:
Infections such as Staphylococcus aureus and tuberculosis initially start as local infections.
The initial infection is often localized to a specific area or organ in the body. In the case of Staphylococcus aureus, it might be a localized skin infection, while TB infections often start in the lungs. From the initial local site, the infection can then spread and become disseminated, potentially affecting other organs or systems in the body. Understanding the progression from a local to a systemic infection is crucial for effective diagnosis and treatment.
For example, a hair follicle infected by Staphylococcus aureus may result in a boil around the site of infection, but the bacterium is largely contained to this small location.
Similarly, in the case of tuberculosis, the infection initially affects the lungs before spreading to other parts of the body.