Pneumonia is a breathing (respiratory) condition in which there is an infection that inflames the air sacs in one or both lungs. The air sacs may fill with fluid or pus (purulent material), causing cough with phlegm or pus, fever, chills, and difficulty breathing. Pneumonia may be caused by bacteria, viruses, fungi, or chemical irritants.

Diagnosis is usually made based on your recent health history, and your healthcare provider may diagnose pneumonia with a thorough history and physical exam.