Pneumonia is an infection in one or both lungs that causes inflammation and the air sacs (alveoli) to fill with fluid or pus, making it difficult to breathe. It can be caused by bacteria, viruses, or fungi, and the severity of the illness can range from mild to life-threatening. Common symptoms include cough, fever, chills, and trouble breathing. Pneumonia is especially serious for infants, young children, older adults, and people with weakened immune systems. Treatment varies depending on the cause and severity, and there are vaccines available to help prevent some types of pneumonia.
