MRSA: Overview
MRSA is a common bacterial infection of the skin, soft tissues, and respiratory tract. It is caused by a bacterium called Staphylococcus aureus that is resistant to multiple common antibiotics, including penicillin; methicillin-resistance is a marker for multi-drug resistance.
Examples of skin infections include folliculitis, boils and cellulitis. Staphylococcus aureus normally lives on the skin surface as well as inside the nose, mouth, throat and GI tract.
Individuals who demonstrate positive MRSA cultures but do not have active infection are called “MRSA carriers.” Of the individuals who carry MRSA, nasal cultures are positive in 50%; when performed in conjunction with nasal samples, cultures of the groin, axilla, and throat will detect 96% of all MRSA carriers.
Certain MRSA strains may be particularly contagious, including the USA 300 and USA 400 strains. MRSA can be acquired by a handshake or by direct exposure to personal items or body fluids from a colonized/infected individual; the ease with which MRSA can be spread between individuals makes community re-exposure commonplace and reinforces the need for good handwashing after public contact.
MRSA: Risk Factors
MRSA typically causes hospital-acquired infection, including pneumonia, bedsores, sepsis from intravenous catheters, orthopedic infections following trauma and joint replacement surgery.
In recent years more MRSA infections are being detected in community settings; three main risk factors warrant consideration: (i) recent exposure to healthcare settings, (ii) close physical contact with others, and (iii) medical conditions that increase risk for staphylococcal infections.
Additional risk factors include hemodialysis treatment, exposure to daycare centers, incarceration, military service, contact sports (e.g., wrestling), and close physical contact with an infected individual.
Certain medical conditions may make individuals more prone to develop MRSA, including diabetes, IV drug addiction, immune disorders (e.g., cancer chemotherapy), HIV infection, chronic skin diseases (e.g., psoriasis) and chronic wounds due to vascular disease or diabetes.
Pets are an uncommon source of MRSA, although farmers may be at higher risk. Anywhere between 1% and 50% of the normal population can carry MRSA, depending on the above risk factors.
MRSA: Symptoms
Individuals may be unaware that they are carrying MRSA until they develop an infection or a screening culture is performed in a healthcare facility.
Folliculitis and skin abscesses (also called boils or furuncles) may be caused by Staphylococcus aureus (either MRSA or methicillin-susceptible strains).
Examples of staphylococcal skin infections are shown in the accompanying photographs.
MRSA: Treatment
Medical and Surgical
Cutaneous abscesses (boils) due to MRSA typically require surgical drainage for cure. If there is a significant component of cellulitis, then oral antibiotics are provided concurrently.
Less serious infections, such as minor folliculitis can be treated with a combination of chlorhexidine soap, topical mupirocin ointment, and warm compresses to affected areas to encourage drainage. When there is more extensive infection, then oral doxycycline, trimethoprim-sulfamethoxazole (Bactrim), or clindamycin (when susceptible), may be appropriate.
Purulent drainage from pustules or boils tends to distinguish between “staph” and “strep” infections, with the former demonstrating pus formation and the latter demonstrating more rapid spreading cellulitis or red streaks up the extremities following trauma (also called lymphangitis).
Decolonization
Due to the many possible sources for MRSA in the environment and community, each person’s condition must be evaluated individually. Screening for problems with the immune system may be needed in case of repeated infection.
Patients with recurrent MRSA infections may require a process called “decolonization,” where the Staphylococcus aureus germ is eliminated from the nose and skin surfaces through topical and/or oral antibiotics.
In some cases, oral antibiotics (either Bactrim or doxycycline, sometimes combined with rifampin) may need to be given concurrently to eliminate the carrier state.
Other household members (e.g., spouse) may be colonized with MRSA and serve as a source of re-infection for a susceptible individual, even if the household member demonstrates no signs of active infection themselves.
The latter is accomplished through whole-body chlorhexidine baths and application of nasal mupirocin ointment twice daily for 10 days.
Prognosis
Most individual episodes of MRSA infection are curable, but recurrence is common.
MRSA carriers in the community can re-introduce MRSA into households through multiple potential mechanisms. Rescreening and decolonization may be needed in case of repeated MRSA infection.
Addressing individual risk factors, such as treatment for diabetes, chronic wounds, and skin diseases are also necessary to reduce the risk of re-infection.
Based in Princeton-Plainsboro, New Jersey, Arunima Mamidi M.D. and team provides personalized medical care to their patients.
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