Which of the following is a common sign of infection?

Fever is a common sign of infection because it indicates the body's immune response to an invading pathogen. When the body detects an infection, the hypothalamus in the brain raises the body's temperature as a defense mechanism, creating an environment that is less favorable for the growth of microbes. Elevated body temperature, or fever, can also enhance the activity of white blood cells, assisting in fighting off infections more effectively. It serves as an important clinical indicator that something is wrong, prompting further investigation and potential treatment.

While a cough, swelling, and pain can also indicate an infection, they are not as universally applicable as fever. For instance, a cough might suggest a respiratory infection, swelling is often associated with localized infections or inflammation, and pain can be a symptom of various conditions, not just infections. Thus, fever stands out as a classic systemic response to infection that clinicians routinely monitor.