In empirical therapy, a patient has proven or suspected infection, but the responsible microorganism is not yet unidentified. While the microorgainsim is being identified the doctor will usually administer the best choice of antibiotic that will be most active against the likely cause of infection usually a broad spectrum antibiotic. Empirical therapy is usually initiated before the doctor knows the exact identification of microorgansim causing the infection as the identification process make take several days in the laboratory.