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Organisms causing HAIs


Infectious organisms

A variety of organisms, including bacteria, viruses, and fungi, cause healthcare-associated infections or HAIs. Some of the organisms are naturally part of the body but can cause an HAI when they move into a normally sterile part of the body as a result of medical care.  For example, Staphylococcus aureus (Staph aureus) is one of many bacteria that commonly live on the skin of many individuals. If there is a break in the skin the organisms may enter below the skin where it is normally sterile and cause an infection, such as a boil.

Drug-resistant organisms

Antimicrobial agents and antibiotics are used to treat infections, including HAIs. Some organisms develop resistance to these drugs and are called "drug resistant." When resistance develops to more than one agent they are known as "multi-drug resistant organisms" (MDRO). When the antimicrobial agent is effective in treating HAIs, the organisms is called drug sensitive or susceptible. Any organism, whether single drug resistant, MDRO, or drug sensitive/susceptible, has the potential to cause HAIs, including serious infections. MDROs are of particular concern because of more limited options for treatment and increased mortality and costs of care. Two examples of drug sensitive organisms that may cause serious infections are Group A streptococcus and C. difficile.

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Staphylococcus aureus and MRSA

A Staphylococcus aureus infection can be caused by an organism that is sensitive or resistant to an antibiotic called "methicillin-sensitive Staph aureus" (MSSA) or "methicillin-resistant Staph aureus" (MRSA).  Recent data show that MSSA cause half of the surgical site infections reported to CDC and that MRSA has been increasing in prevalence in both the hospital and community settings. Regardless of the causative organism, antibiotic resistance pattern, type of infection, or source of infection, the goal is the same -- the elimination of all HAIs. For more information see:

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