What is pneumonia? Pneumonia is a general term for a variety of diseases that cause an inflammation of the lungs. Pneumonia is most often caused by a bacterial infection (bacterial pneumonia) or a viral infection (viral pneumonia). Typical symptoms of pneumonia include fever, shortness of breath, and a wet cough that produces thick white, yellow, green or brownish phlegm. Pneumonia is a common disease that can occur at any time of the year. It can occur in almost any population but is most common in smokers and people who have chronic infections and diseases, such as: Acute bronchitis Asthma Congestive heart failure Emphysema or chronic obstructive pulmonary disease (COPD) Lung cancer In generally healthy adults, pneumonia can be a relatively moderate condition and not require hospitalization. However, pneumonia is a common complication of a variety of diseases and can lead to life-threatening complications, such as sepsis and respiratory failure. Pneumonia is a frequent cause of death, especially in infants and older adults with chronic diseases, or people who have immune systems that are weakened as a result of such conditions as HIV/AIDS. Seek prompt medical care if you have symptoms of pneumonia, such as fever and a wet cough that produces white, yellow, green or brownish phlegm. Seek immediate medical care (call 911) if you, or someone you are with, have moderate to severe shortness of breath, bluish coloration of the lips or fingernails, or a change in level of consciousness or alertness.