Which of the following is a common symptom of an infection?

Fever is a common symptom of an infection as it is part of the body's natural defense mechanism. When a person has an infection, the immune system responds by raising the body's temperature, which can help to inhibit the growth of pathogens and facilitate the healing process. A fever signals to the body that it is fighting off an invader, such as bacteria or viruses, and can often be accompanied by other symptoms.

While the other options may indicate an underlying health issue, they are not as universally recognized as hallmarks of infection. Difficulty breathing can be associated with respiratory infections but is not exclusive to infectious causes. A rash may occur due to various dermatological conditions, including infections, but can also arise from allergic reactions or other non-infectious conditions. Weight loss might be seen in chronic infections or conditions, but it is not an immediate or typical symptom of infection on its own. Therefore, fever is the most direct and common symptom associated with infections.