Diagnostic tests are designed to determine which microbe is causing infection and to which antimicrobials the microbe might be resistant. This information would be used by a healthcare provider to choose an appropriate antimicrobial treatment. However, current diagnostic tests often take a few days or weeks to give results. This is because many of today's tests require the microbe to grow over a period of time before it can be identified.
Oftentimes, healthcare providers need to make treatment decisions before the results are known. While waiting for test results, healthcare providers may prescribe a broad-spectrum antimicrobial when a more specific treatment might be better. The common practice of treating unknown infections with broad-spectrum antimicrobials can accelerate the emergence of antimicrobial resistance.