Pneumonia is an infection that inflames your lungs' air sacs (alveoli). The air sacs may fill up with fluid or pus, causing symptoms such as a cough, fever, chills and trouble breathing.
The World Health Organization (WHO) recognizes four features as danger signs in pneumonia. They include stridor, fast breathing, chest wall indrawing, and difficulty in breathing (labored breathing).
Bacteria are a common cause of pneumonia in adults. Many types of bacteria can cause pneumonia, but Streptococcus pneumoniae (also called pneumococcus bacteria) is the most common cause in the United States.