Pneumonia is an infection that inflames the air sacs in one or both lungs, which can fill with fluid or pus. This condition can be caused by various organisms, including bacteria, viruses, and fungi. Symptoms often include cough, fever, chills, and difficulty breathing. Pneumonia can affect anyone, but it is particularly serious for young children, the elderly, and individuals with weakened immune systems. Diagnosis typically involves a physical examination, chest X-rays, and sometimes laboratory tests to identify the causative agent. Treatment may include antibiotics for bacterial pneumonia, antiviral medications for viral pneumonia, and supportive care to help with breathing. Vaccines are available to help prevent certain types of pneumonia, such as those caused by the Streptococcus pneumoniae bacteria.