Which of the following is a sign of infection?

Fever is a well-known clinical indicator of infection as it reflects the body's immune response to pathogens. When the body detects an infection, it often raises its temperature as a defense mechanism. This increase in body temperature is typically regulated by the hypothalamus, which releases substances called pyrogens in response to infection. Fever can aid in fighting off infections by creating an environment less conducive to the growth of bacteria and viruses.

Although cough, fatigue, and shortness of breath can also be associated with various infections, they are not specific signs of an infection on their own. Cough can occur due to a range of irritants, including allergies or respiratory conditions unrelated to infections. Fatigue can result from various physical and psychological factors that are not solely tied to infection. Similarly, shortness of breath can arise from many respiratory or cardiovascular conditions, which may or may not be related to infectious processes. Thus, fever stands out as a more direct and specific sign of infection.