Which of the following is a sign of infection?

An increased temperature, commonly known as a fever, is a well-known sign of infection. When the body recognizes the presence of pathogens such as bacteria or viruses, it often responds by raising its internal temperature in an attempt to create an environment that is unfavorable for the pathogens while enhancing the body’s immune response. This elevation in temperature is a physiological reaction to infection and serves as a critical indicator when assessing a patient’s health status.

The other symptoms listed—slight headache, reduced appetite, and fatigue—can occur for a variety of reasons, including other medical conditions, stress, or even lack of sleep, and are not specific indicators of infection on their own. Thus, while they may accompany an infection, they do not directly signal its presence as clearly as an increased temperature does.