Sputum is material coughed up from the lungs and spit out through the mouth. A sputum culture is done to find and identify the germ causing an infection such as pneumonia (an infection of the lung). If a specific germ is found, more testing is done to determine which antibiotic will best treat the infection.

A person with a fever and a continuing cough that produces pus-like material or blood may have an infection of the lungs and bronchial tubes. These infections are caused by several types of germs, including bacteria, fungi (molds and yeast), and viruses. A chest x ray helps a doctor see the infection; a culture can grow the germ causing the infection so it can be identified.

Based on the symptoms, the doctor decides what group of germ is probably causing the infection, and then orders one or more specific types of...