Which of the following is a symptom of infection?

Swelling and redness are hallmark signs of infection, particularly evident in the area where the infection is localized. This occurs as the body’s immune response kicks in; white blood cells and other substances rush to the site to combat pathogens, leading to increased blood flow and resulting in inflammation, which manifests as swelling and redness. This physiological response is crucial as it helps the body respond to and heal from the infection.

The other choices do imply symptoms but are not as directly indicative of infection as swelling and redness. Decreased appetite can occur for various reasons, including illness or stress, but is not a specific symptom of infection. Coughing may indicate respiratory issues, which could be related to an infection, but it is not exclusive to infections. Improved energy levels typically indicate recovery or good health, which contradicts the idea of an ongoing infection. These distinctions further highlight why swelling and redness are considered classic symptoms of infection.