MRSA, (methicillin-resistant staphylococcus aureus), is a form of bacterial infection that is resistant to numerous antibiotics including methicillin, amoxicillin, penicillin and oxacillin, thus making it challenging to treat the infection successfully.1
Often referred to as a superbug, MRSA infection may commence as a minor skin sore, pimple or boil, before becoming serious, potentially harmful and sometimes fatal.
Contents of this article:
You will also see introductions at the end of some sections to any recent developments on MRSA that have been covered by MNT's news stories. Also look out for links to information about related conditions.
Fast facts on MRSA
Here are some key facts about MRSA. More detail and supporting information is in the main article.
- MRSA is a form of bacterial infection that is resistant to numerous antibiotics.
- MRSA infection can begin as a minor skin sore or pimple and become potentially harmful.
- "Methicillin" represents the antibiotic that was once effective against staphylococci (staph).
- "Staphylococcus aureus" refers to a bacterium that commonly resides inside the nose and human skin.
- Around one in three (33%) people carry staph in their nose, usually without any illness. Two in 100 people carry MRSA.
- MRSA can be divided between health care associated MRSA and community associated MRSA.
- Annually, there are around 94,360 invasive MRSA infections diagnosed in the US, with 18,650 associated deaths.
- It is estimated that 49-65% of health care associated S. aureus infections are caused by methicillin-resistant strains.
- Invasive health care associated MRSA infections declined by 54% between 2005 and 2011.
- Approximately 86% of all invasive MRSA infections are contracted with health care settings.
- Germ-killing soaps and ointments used in intensive care units have been found to reduce MRSA cases by 40%.
What is MRSA?
"Methicillin" represents the semisynthetic penicillin-related antibiotic once effective against staphylococci (staph).2 Staph bacteria have developed a resistance to penicillin-related antibiotics, including methicillin - these resistant bacteria are called methicillin-resistant staphylococcus aureus, or MRSA.
"Staphylococcus aureus" (S. aureus) refers to an often harmful bacterium, commonly found in the nose and skin of humans.3 In the US, staph bacteria are one of the most common causes of skin infections. Although 33% of the population is colonized with staph (bacteria is present but not causing infection), around 2% of the population is colonized with MRSA.10
MRSA, full name methicillin-resistant staphylococcus aureus, is a form of bacterial infection that is resistant to numerous antibiotics including methicillin, amoxicillin, penicillin and oxacillin.
The bacterium that can cause staph skin infections can divide every half-hour in optimum conditions. Theorectically, a single cell can form a colony of more than a million cells in 10 hours.5
S. aureus can cause skin infections including:
Staph bacteria can also enter the body, and invade the bloodstream through broken or damaged skin or during medical procedures, and can cause infections and resulting conditions that range from mild to severely life-threatening. These conditions may include:
- Septicemia (blood poisoning)
- Pneumonia (lung infection)
- Osteomyelitis (bone infection)
- Endocarditis (heart valve infection)
- Urinary tract infection (eg. bladder infection)
- Septic bursitis (small fluid-filled sacs under the skin).
Around 94,360 invasive MRSA infections are diagnosed annually in the US, with 18,650 associated deaths. MRSA infections are typically classified as health care-associated or community-associated, with approximately 86% of all invasive MRSA infections health care-associated.6
Causes of MRSA
Ultimately MRSA is caused by bacterium strains that have acquired a resistance to particular antibiotics.
MRSA can spread from person to person (skin-to-skin contact) and from person to object to person when an individual has active MRSA or is colonized by the bacteria.
Skin-to-skin contact with someone carrying MRSA is not necessary for infection to spread. MRSA bacteria are also able to survive for extensive periods on surfaces and objects including door handles, floors, sinks, taps, cleaning equipment and fabric. One study to determine the survival of resistant staph on common hospital surfaces looked at staph survival on five materials commonly found in hospital:8
- 100% smooth cotton (clothing)
- 100% cotton terry (towels and wash cloths)
- 60% cotton-40% polyester blend (scrub suits, lab coats and clothing)
- 100% polyester (privacy drapes, curtains and clothing)
- 100% polypropylene plastic (splash aprons).
Swatches of fabric were injected with 10,000 to 100,000 colony-forming units (CFU) of the microorganism and observed daily. Results showed S. aureus survived on the materials for the following number of days:
- Cotton: 4-21 days
- Terry: 2-14 days
- Polyester blend: 1-3 days
- Polyester: 1-40 days
- Polypropylene: 40-greater than 51.
These results conclude the need for thorough contact control and meticulous disinfection procedures to limit spread of bacteria.
Health care-associated MRSA
MRSA frequently causes illness in people with a compromised immune system who interact with or reside in hospitals and health care facilities. This is referred to as health care-associated MRSA (or hospital-acquired MRSA) and often occurs for one of the following reasons:4
MRSA bacteria have the aptitude to survive for extensive periods on surfaces and objects in hospitals including door handles, floors, sinks, taps, cleaning equipment and fabric.
- A break in the skin barrier, such as a surgical wound, burn, catheter or intravenous line that allows bacteria to enter the body
- Older age, comorbidities or multiple complex health issues, and weakened immune systems due to a specific health condition or the use of medications that lower immune function
- The simple fact that hospitals and health care facilities are visited by large numbers of people, both patients and staff, providing an environment for bacteria to easily spread from person to person or person to object to person.
Those with a weakened immune system can include:
- Patients in hospital for a long period of time
- Patients on kidney dialysis (hemodialysis)
- Patients receiving cancer treatment or specific medications that affect immune function
- Those who inject illegal drugs
- Individuals who have had surgery within a year of being back in hospital.
Estimates suggest that 49-65% of health care-associated S. aureus infections are caused by methicillin-resistant strains.6
According to the Centers for Disease Control and Prevention (CDC) study, invasive health care-associated MRSA infections declined 54% between 2005 and 2011, with 30,800 fewer severe MRSA infections and 9,000 fewer deaths.9
A similar study conducted by the National Healthcare Safety Network (NHSN) found that rates of health care-associated MRSA bloodstream infections fell nearly 50% from 1997-2007.10
The average age of a person with health care-associated MRSA was 68.11
Who is at risk?
People most at risk of developing health care-associated MRSA in the hospital include those that have:
- Weakened immune systems
- Open wounds
- A catheter or intravenous drip inserted
- Burns or cuts to the skin surface
- Severe skin conditions
- Had surgery
- Frequent antibiotics as part of their treatment.
Community-associated MRSA is contracted external to the hospital and is less widespread compared with health care-associated MRSA. Factors that cause increased risk of developing community-associated MRSA include:4
Regular skin-to-skin interaction for example in contact or collision sports such as rugby, ice hockey, soccer and basketball cause an increased risk of developing community-associated MRSA.
- Living in an environment with a lot of people; military bases, jail, on-campus housing
- Regular skin-to-skin interaction for example in contact or collision sports such as rugby, ice hockey, soccer and basketball
- Cuts or grazes to the skin or regular injection of drugs
- Contaminated surfaces
- Unhygienic facilities or lack of personal hygiene
- Previous antibiotics use.
The CDC reports that 14% of people with MRSA infections contracted them outside of the health care setting.
The average age of a person with community-associated MRSA was 23.11
The 5 Cs can be used to remember what factors make it easier for MRSA to be transmitted:4
- Contact (skin-to-skin)
- Compromised skin (open wounds)
- Contaminated (items and surfaces)
- Cleanliness (lack of).
Recent developments on MRSA causes from MNT news
Researchers have found that wearing gloves and gowns in intensive care units does not reduce overall rates of acquiring MRSA or VRE, a study published online by JAMA has revealed.
A new study has suggested that a type of MRSA found in humans may have originated from cattle as far back as 40 years or more.
On the next page we take a close look at symptoms of MRSA, what antibiotic resistance means and the available tests and diagnosis options. On the final page we discuss treatment and prevention of MRSA.