An Overview of Hospital-Acquired MRSA (HA-MRSA)

A.K.A. Healthcare-Acquired MRSA

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Hospital-acquired methicillin-resistant Staphylococcus aureus, also known as healthcare-acquired MRSA or HA-MRSA, is a potentially deadly strain of staph bacteria. This superbug, resistant to many antibiotics, has long been a public health concern, with no less than 60% of hospitals in the United States reporting one or more incidents of HA-MRSA in 2013.

Despite inordinately high rates of infection in the latter part of the 20th century, there has been a slow decline of MRSA diagnoses since then due to increased awareness and a rigorous adherence to universal precautions in healthcare settings.

Microbiologist holding a culture plate of an MRSA
Rodolfo Parulan Jr / Getty Images


MRSA infections can appear as a small red bump, pimple, boil, or abscess. The affected area may be warm, swollen, or tender to the touch. Fever may also accompany this. Less commonly, an MRSA infection can cause chest pains, chills, fatigue, headache, or rash.

Most MRSA infections are mild, but some can spread and become systemic (involving the whole body). This can lead to potentially life-threatening infections of bones, joints, heart valves, lungs, and the bloodstream.

Among some the possible complications of MRSA infection are:

HA-MRSA infections are generally defined as those that develop within 48 hours of discharge from a hospital, clinic, or healthcare facility.


There are many different variations of staph bacteria. Most are relatively harmless and usually only cause minor skin problems in healthy people.

However, with the widespread, inappropriate use of antibiotics around the world, mutated strains of Staphylococcus aureus have begun to emerge, many of which are resistant to a broad spectrum of antibiotic drugs.

Anyone can get MRSA. The risk increases in places where people regularly gather and either have skin-to-skin contact or exposure to shared equipment or supplies. The risk is further increased if there is broken or non-intact skin.

How Resistance Develops

Staphylococcus aureus, like all bacterium, are prone to mutations. Most of these mutations are harmless and result in weak bacteria that are unable to survive. On the odd occasion, however, a mutation may result in a drug-resistant strain.

Even if this occurs, it won't usually undermine the effectiveness of an antibiotic since it won't be the predominant strain. This can change, however, if antibiotics are overprescribed or used improperly.

For example, if you are on a seven-day course of antibiotics and stop prematurely before an infection is fully resolved, the predominant strain—the type most sensitive to antibiotics—will be neutralized but not the resistant one. The more and more that this pattern is repeated, the larger the resistance population will become, filling the gap left by the predominant bacteria and eventually becoming dominant itself.

As a resistant bacterium is passed from person to person, it can pick up additional mutations from those who have been inappropriately treated with other types of antibiotics. Over time, the antibiotic-resistant bacterium may evolve into a fully multi-drug-resistant superbug.

How MRSA Infections Are Established

Staphylococcus aureus is uniquely suited to survive. Its external protein shell (capsid) is dense enough to live outside of the human body for days or weeks and sticky enough to adhere to different surfaces, including the skin.

Staphylococcus aureus also secretes a variety of proteins that either inhibit or kill white blood cells that the body uses to neutralize disease-causing microorganisms. By doing so, the bacteria can evade the front-line immune assault and quickly establish an infection.

In hospital settings, Staphylococcus aureus can form a slimy material, called a biofilm, that serves as a protective barrier against even the more potent antimicrobial agents.

In addition, many of the symptoms of MRSA occur as a result of tissue destruction by enzymes secreted by the bacterium. Among other things, Staphylococcus aureus secretes a type of toxin, classified as a superantigen, that allows it to penetrate the skin more readily and enter the bloodstream, increasing the risk of sepsis and septic shock.

Risks in Hospitals and Other Healthcare Settings

Hospitals and healthcare facilities pose the greatest risk of person-to-person transmission of superbugs like MRSA. HA-MRSA infections frequently occur in these settings for several reasons:

  • These are sites where a large stream of people come and go.
  • People regularly undergo invasive procedures, have open wounds, and/or have significantly weakened immune systems due to illness.
  • Failure to wash hands and surfaces frequently can foster the spread of MRSA in settings like these.

Many hospital patients are carriers of HA-MRSA even though they do not have symptoms. Transmission can also occur when a healthcare worker touches one patient and then another without washing their hands or using barrier protection (like disposable latex gloves). Other sources of transmission include catheters, breathing tubes, bed linens, and bed rails.

Infection Rates

According to a 2019 report issued by the Centers for Disease Control and Prevention (CDC), Staphylococcus aureus caused well over 110,000 bloodstream infections in the United States in 2017, resulting in nearly 20,000 deaths. As distressing as these numbers sound, they represent a steady decline from the 1990s when MRSA infections appeared out of control.

Due to improved surveillance and infection control practices, the rate of MRSA diagnoses in the United States dropped by an average of 17.1% annually from 2005 to 2012. While the decline has been less dramatic in more recent years, dropping by an average of 6.9% annually from 2013 to 2016, most of the advances have been attributed to lower rates of infections in hospitals.


MRSA is diagnosed by checking a tissue sample or nasal secretions for signs of drug-resistant bacteria. Traditional tests are cultured in a lab to see if the suspected bacteria are present and can usually return results in 48 hours. Newer DNA tests can return results in a matter of hours.

Depending on your symptoms, your healthcare provider may recommend additional tests, such as blood culture, drainage from the infection, skin culture, sputum culture, or urine culture, to diagnose complications of HA-MRSA.


HA-MRSA is resistant to beta-lactam antibiotics. These include penicillin and its derivatives, cephalosporins, monobactams, carbapenems, and carbacephems. This means that many of the more commonly prescribed antibiotics, like methicillin, amoxicillin, penicillin, and oxacillin, will have little to no effect on the bacteria.

Fortunately, HA-MRSA can still be treated with other types of antibiotics, including clindamycin, linezolid, tetracycline, trimethoprim-sulfamethoxazole, or vancomycin. The choice will depend largely on the MRSA strain prevalent in the region and the severity of the illness.

The standard duration of antibiotic therapy for an HA-MRSA infection is between seven and 10 days. Serious infections may require longer treatment and intravenous (IV) drug delivery.

In some cases, however, antibiotics may not be needed. For example, your healthcare provider may opt to drain a superficial abscess rather than treat the infection with antibiotics. This antibiotic-sparing approach recognizes that antibiotics are not necessarily needed if an infection is mild and your immune system is strong.

Serious infections requiring hospitalization may also involve therapies and procedures to treat MRSA complications. Examples include kidney dialysis in cases of acute kidney failure and oxygen therapy in cases of severe pneumonia.


To prevent getting or spreading MRSA, there are some simple precautions you should take during and after your stay in a hospital or other healthcare facility:

  • Wash your hands often: Wash thoroughly between the fingers and under the nails with soap and warm water or an alcohol-based hand sanitizer.
  • Avoid contact with other people's wounds: If you accidentally touch a wound, wash your hands immediately and avoiding touching surfaces, yourself, or others until you do.
  • Do not share personal care items: This includes towels, razors, skincare products, washcloths, and clothing.
  • Avoid walking with bare feet: Even if you need to go to the bathroom in the middle of the night, wear slippers with non-absorbent soles.
  • Keep your wounds covered: Once home, change your bandages regularly (per your healthcare provider's instructions) using fresh bandages and cleaning the skin thoroughly with the appropriate antimicrobial agent, like Betadine solution (povidone-iodine).
  • Dispose of bandages and tape promptly: Do not wait for others to clear them for you. The fewer hands that are involved, the better.
12 Sources
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Additional Reading

By Ingrid Koo, PhD
 Ingrid Koo, PhD, is a medical and science writer who specializes in clinical trial reporting