How can i tell if i have the common cold (with bronchitis), flu or pneumonia?

Not so easy: Pneumonia is an infection of the lung or lower respiratory tracts. A cold (usually caused by viruses) is an infection of the upper respiratory tract - flu also usually affects the upper tract but can start involving the lungs (serious). A patient should see a physician who can do lab tests and get an x-ray - doubly important to do so if a person is getting worse, dehydrated, or short of breath.