Antimicrobial agents have been used since the 1940s to treat patients who have infectious diseases. However, over time and due to increasing use of these drugs in humans, animals, and agriculture, many bacteria, fungi, viruses, and parasites have adapted to them, making the drugs less effective. Some microorganisms may develop resistance to a single antimicrobial agent (or related class of agent), while others develop resistance to several antimicrobial agents or classes. These organisms are often referred to as multiple drug resistant organisms (MDRO). In some cases, the microorganisms have become so resistant that no available antibiotics are effective against them.
Infections with drug-resistant organisms are primarily a problem in hospitals and other healthcare settings, however they can also spread in the community at large. People infected with drug-resistant organisms are more likely to have longer and more expensive hospital stays, and may be more likely to die as a result of the infection. When the drug of choice for treating their infection doesn't work, they require treatment with second- or third-choice drugs that may be less effective, more toxic, and more expensive. This means that patients with an antimicrobial-resistant infection may suffer more and pay more for treatment.