CAP is defined as a pneumonia originating from the community, with signs and symptoms of acute infection plus an acute infiltrate on the chest X-ray, or auscultatory findings. The consensus among Respiratory Societies is that a chest X-ray showing signs of a new or changing infiltrate is required for a definite diagnosis of CAP. However there is recognition that for those patients treated in the community setting, it may be impractical to insist on a chest X-ray in all instances.