Pneumonia is an infection caused by bacteria or viruses that inflame the air sacs in one or both lungs, which may fill with fluid. For most people, pneumonia can be treated at home; it often clears up in two to three weeks. But older adults, infants and people with other diseases or a weakened immune system can become very ill. In the U.S., about 3 million cases of pneumonia are reported each year, and about 60,000 people die as a result of the condition. About one-third of cases occur in people over age 65. You may be more likely to present symptoms of the disease after having a cold or the flu; these illnesses make it hard for your lungs to fight infection, so it is easier to get pneumonia. Having a long-term, or chronic disease also makes you more likely to contract pneumonia. Symptoms of pneumonia include cough, fever, fast or labored breathing, chills, nausea, diarrhea, chest pain and extreme fatigue.