Lymphadenitis is the inflammation of lymph nodes, often caused by an infection. The lymph nodes, which are part of the lymphatic system, help the body fight infections by filtering harmful substances. When they become infected, they can swell, become painful, and may produce symptoms like fever and fatigue. Common causes of lymphadenitis include bacterial infections, such as strep throat, or viral infections like the common cold. Treatment typically involves addressing the underlying infection, which may include antibiotics for bacterial causes. In some cases, drainage of abscesses may be necessary to relieve symptoms.