Methicillin-resistant Staphylococcus aureus (MRSA) Infections

Author: Helia Mansouri Dana

Editor: Leslie Pineda


Methicillin-resistant Staphylococcus aureus (MRSA) infections are caused by the antibiotic-resistant form of the bacterium Staphylococcus aureus (S. aureus) (Lee et al., 2018). Specific strains of the S. aureus have bacteria acquired antibiotic-resistant genes that have made them resistant to treatment, such as antibiotics (Katayama et al., 2000).

MRSA infections have been on the rise since the 1960s, and continue to make up a large fraction of bacterial infections worldwide (Katayama et al., 2000; Lee et al., 2018). MRSA can cause infections in the lining of the heart, air-sacs, skin, and most dangerously, infections in the blood referred to as bacteremia (Tong et al., 2015).

MRSA infection occurs at different rates across the globe but is typically present in 10-30% of the population (Hassoun et al., 2017). It is typically classified into two main types:

  • Community-acquired MRSA – occurs in healthy individuals as skin infections
  • Hospital-acquired MRSA – acquired in health-care settings following surgery and insertion of medical devices such as catheters

(Tong et al., 2015)


What Causes MRSA Infections?

MRSA infections are caused by specific strains of bacteria called Staphylococcus aureus (abbreviated S. aureus), which contain a gene for resistance against antibiotics such as penicillin and methicillin (Katayama et al., 2000).

S. aureus are naturally found in the nasal cavities in 30% of the population, but they exist without inflicting any harm (Krismer et al., 2017). However, these bacteria may cause disease if they gain access to the underlying tissues or via entry into the blood, leading to bacteremia (Tong et al., 2015).

These bacteria may persist in other environments, such as those in hospitals, and can be largely transmitted to patients during recovery after procedures by contaminated hands of health care staff, or at insertion sites of medical catheters (Fernando et al., 2017).

In the community-acquired type of MRSA, infections happen via transmission with skin-to-skin contact, and mainly leads to skin infections, though in a small percent of individuals, the infection may spread to the rest of the body where it causes pneumonia or bacteremia, a condition where bacteria gain access to the blood (Otto, 2013).



  • Large blisters on extremities or face that progress to dried scabs (skin infections by MRSA)
  • Swollen, red, painful joints (Septic arthritis by MRSA)
  • Inflammation at site of device insertion or attachment (Device-related MRSA infections)
  • Redness, an increase in skin roughness, and pus formation at site of device insertion or attachment (Device-related MRSA infections)
  • Fever (bacteremia or other types of MRSA infections)
  • Coughing and sore throat (pneumonia by MRSA)

(Tong et al., 2015)


Risk Factors

  • Prior existence of MRSA in the body, even as harmless bacteria in the nose
  • Discharge of patients to nursing homes, where MRSA strains may get transmitted from staff  
  • Environments such as hospitals and intensive care units, transmitted from health care staff
  • Chronic wounds – allow easy access of bacteria into the blood
  • Usage of invasive devices such as catheters and hemodialysis machines – allow access of bacteria into the blood as they use needles inserted into the main veins of the body

(Epstein et al., 2016)



Different types of MRSA infections have different clinical presentations, and some may even be asymptomatic.

Infections of the skin present as large blisters that progress into large, dried scabs (Tong et al., 2015). Symptoms of inflammation such as swelling, pain, redness and heat may also be seen if the infection is related to insertion of medical devices (Sahli et al., 2017).

In more severe cases, the symptoms are often unclear and broad, such as fever (Yang & Frazee, 2018). Urinary catheters further lead to UTIs which are associated with fever (Muder et al., 2006).

If you are experiencing joint inflammation, pain, and limited range of motion, it could be an indication of joint infections via MRSA, though further testing is required (Shirtliff & Mader, 2002)

This involves testing for the presence of MRSA strains in soft tissue or blood in order to confirm diagnosis, and to further allow moving forward with a treatment plan. This typically involves blood testing and biopsies to test for presence of the bacteria that cause the infection by culturing and antibiotic testing (Palavecino, 2020).



Hospital-acquired MRSA

Treatment involves the removal of any source of infection, for example, CVCs or urethral catheters, or any other device that has caused the MRSA infection (Hassoun et al., 2017).

If you have recently received valve replacement surgery and are diagnosed with MRSA infections, subsequent surgery may be needed to replace the valve (Hassoun et al., 2017). Surgery may also be required for patients with infections of the lining of the heart, as it may have caused extensive damage (Yang & Frazee, 2018). For treatment of MRSA bacteremia, vancomycin and daptomycin are recommended via intravenous administration (Lewis et al., 2018)


Community-acquired MRSA

Treatment involves insertion and drainage of skin blisters or pus-filled sacs on the skin caused by the bacteria, and a type of antibiotic drug called Trimethoprim/Sulfamethoxazolen or TMP/SMX is recommended for oral use (Creech et al., 2015).

If infections are more severe however, such as the presence of bacteria in the blood, the same treatments mentioned above would be suggested (Lewis et al., 2018).



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