MRSA Transmission – How MRSA Spreads

Health care professionals are exposed to increasing numbers of patients with MRSA colonization or infection from both acute care and long-term care facilities. As MRSA is estimated to affect tens of thousands of people, costing the health care system $4-5 billion annually, awareness of MRSA and the sources of MRSA transmission has been steadily growing.

It is estimated that between 30-40% of the population are colonized with Staphylococcus aureus. A growing percentage of these people are carriers of an antibiotic resistant strain, generally referred to as Methicillin-resistant Staphylococcus aureus (MRSA) . MRSA is a type of Gram-positive bacteria that has evolved to become resistant to many first and second line antibiotics, including the beta-lactams. There are two classifications of MRSA based upon the source of infection. The most common form of MRSA infection is hospital or healthcare-associated MRSA (HA-MRSA); the second less common but growing form is community-associated MRSA (CA-MRSA).

MRSA transmission occurs during direct contact with contaminated food, surfaces, objects , animals and people1 who are either infected or colonized with MRSA (carriers but not suffering from active infection). Transmission can occur either by touching contaminated people or objects as well as from exposure to the tiny nasal spray droplets expelled during exhalation by MRSA contaminated people or animals. It is believed that the majority of transmissions occur by direct person-to-person contact. Furthermore, studies are now showing that self-infection by those carrying MRSA is a significant risk.

People who are colonized with MRSA carry the bacteria either on their skin or inside their noses. S. aureus and MRSA can survive almost anywhere on the body, but MRSA favours warm moist, protected areas such as the nose, armpits, anus, groin and pubic areas.  Common inanimate sources of MRSA in hospitals are toilet seats, faucets, beds, t.v, remote controls, stethoscopes, computer keyboards and blood pressure cuffs. Common inanimate sources of MRSA in communities include shared personal items such as sports equipment, towels, linens, razors, uniforms and makeup. For this reason, MRSA transmission is commonly observed in prisons, institutions, military and athletic settings.

It is estimated that 5% or more of the general population may be asymptomatic carriers of MRSA. This is broken down into about 7% of people in hospitals and about 2% of people in the community. High risk people such as patient-facing health care workers, nursing home patients and dialysis machine dependents may be as high as 25% carriers. Carriers can remain colonized for years and represent a growing risk to the community. Carriers are a major source of transmission and represent a concern since it is not obvious or apparent who may be colonized with MRSA.  Moreover, carriers are also at risk of self-infection, especially when their immune systems are compromised such as after a major surgery or when they have open wounds, cuts or abrasions.

Any break in the skin (e.g. rashes, open sores, fungal infections, bed sores, surgical sites, catheter points) are an access opportunity for this opportunistic bacteria. Although someone may be infected with MRSA, they may not develop any signs or symptoms of the infection for up to 10 days.2 Active prevention protocols therefore include thorough disinfection of surfaces and decolonization protocols which target elimination of MRSA carriage through use of infection control measures, antibiotics, and newer non-antibiotic technologies such as photodisinfection. Decolonization measures have been proven to reduce the risk of transmission to high-risk people who are immunocompromised or highly susceptible to infection. Due to its ability to resist the affects of methicillin, oxacillin and many other antibiotics, the current antibiotic of choice is intravenous vancomycin (often considered one of the last resort antibiotics). Oral vancomycin, however, is generally regarded as not being effective against MRSA. 3

  1. Juhasz-Kaszanyitzky et al . MRSA Transmission Between Cows and Humans, Emerg Infect Dis 2007 Apri:13(4): 630 -2
  2. EMedTV – http://bacteria.emedtv.com/mrsa/mrsa-transmission.html
  3. Associated for Professional In Infection Control and Epidemiology
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