Hundreds of different microorganisms can infect the lungs, but most cases of pneumonia are caused by viruses or bacteria. Viral pneumonia, which accounts for about half of all cases, is most often a complication of influenza.
In bacterial pneumonia, the onset of symptoms is typically abrupt. Symptoms may include a cough that produces yellow phlegm, high fever, chills, sharp chest pain precipitated by breathing or coughing, and shortness of breath. Young pneumonia patients usually have increased breathing and heart rates and appear acutely ill. Many older adults have fewer pneumonia symptoms, often have no fever, and experience lethargy and confusion with or without lung-related symptoms.
The early symptoms of viral pneumonia may resemble those of infection with the influenza virus: a dry cough, fever, headache, muscle pain, and weakness. Twelve to 36 hours later, people with viral pneumonia often experience increased breathlessness, worsening cough with mucus, high fever, and, possibly, blueness of the lips. People with very serious viral pneumonia may have extreme difficulty breathing.
Antibiotics are the mainstay of treating bacterial pneumonia. Most people with viral pneumonia recover without treatment in one to three weeks. Antibiotics are not effective against viral pneumonia, but if there is any doubt as to the cause of the pneumonia, antibiotics are often prescribed.
When the cause is bacterial, early treatment produces the best outcomes. In one study, elderly pneumonia patients who got antibiotics within four hours of arriving at a hospital were less likely to die than those who had to wait longer.
