MSSA vs. MRSA: What Is the Difference?

October 21, 2019
MRSA Illustration

One of the first known “superbugs,” MRSA has been making headlines since the 1960s. Today, as the list of antibiotic-resistant bacteria grows, MRSA is still a major concern for healthcare providers and communities alike. 

MRSA’s infamous reputation shouldn’t give the impression that MSSA is a kinder, gentler strain of staph infection. The Centers for Disease Control and Prevention (CDC) warns, “MRSA is well known but any staph can be deadly.” 

When it comes to MSSA vs MRSA, the two are more alike than different. They have the same symptoms, cause similar problems, and cost roughly the same amount to treat. There are however, some key differences, including how (and where) the two bacteria tend to spread and how difficult they are to treat.

MSSA vs MRSA: How Are They Different?

MSSA and MRSA are two types of Staphylococcus aureus (or staph), a bacteria that many people carry on their skin and in their noses. Most people don’t even know it’s there, because the bacteria doesn’t make them sick unless a wound, surgery, or IV needle stick gives it an entrance into the body. Then it can cause infections ranging from minor skin conditions to life-threatening sepsis. Infected and “colonized” people can also transmit staph to others. When someone is colonized, S aureus bacteria is living on the individual’s skin.

The defining difference between MRSA and MSSA lies in how they respond to methicillin — an antibiotic that was introduced in 1959 to treat staph infections. Some S. aureus strains had already developed a resistance to penicillin, and by 1961, British scientists discovered strains that resisted methicillin as well. These are called methicillin-resistant staph (MRSA), as opposed to methicillin-susceptible staph (MSSA).

In terms of global health, MRSA is a more serious problem than MSSA because of its ability to evolve. There are even a few strains that can resist vancomycin, one of the last remaining antibiotics for MRSA. That’s why the Centers for Disease Control and Prevention (CDC) lists MRSA as one of the top “Antibiotic Resistance Threats in the United States.”

For individuals, however, both MRSA and MSSA can cause life-threatening staph infections.

Prevalence of MSSA vs MRSA Infection

One in three people (33%) carry staph in their noses, and two percent are colonized with MRSA, according to the CDC. These people are colonized, but most of them rarely become infected. If the staph bacteria gets below the skin’s surface, it can cause painful skin infections, but the real danger is when staph enters the bloodstream. More than 119,000 people were diagnosed with bloodstream staph infections in 2017, and nearly 20,000 of them died as a result. 

Some MRSA strains are more dangerous than others, but according to the World Health Organization (WHO), MRSA is generally not more virulent than MSSA. However, because MRSA is more likely than MSSA to be associated with bacteremia (bacteria in the bloodstream), MRSA has the higher mortality rate. The CDC estimates that 80,461 people experience MRSA infections each year, and 11,285 of them die.

MRSA is the most common cause of hospital-acquired bacteremia, but MSSA can also be deadly in healthcare settings, especially for infants. In a study of 348 neonatal intensive care units across the country, researchers from Duke University found that 72.1 percent of staph infections in hospitalized infants were caused by MSSA. Infants with serious MSSA infections were also more likely to die before discharge than infants with MRSA infections.

The good news is that better screening and prevention protocols have helped U.S. hospitals dramatically decrease staph infection rates since earlier this century. Between 2005 and 2012, MRSA bloodstream infections associated with healthcare facilities decreased by 17 percent per year, according to the CDC

The bad news is that hospitals’ MRSA progress has stagnated, with little improvement since 2013. Meanwhile, MSSA is on the rise in communities, likely due in part to the opioid crisis. In 2016, nine percent of people with serious staph infections injected drugs — up from four percent in 2011. 

Risk Factors for MSSA Infections vs MRSA

Overall, MRSA tends to be associated with hospital-acquired infections, while MSSA tends to be associated with community-acquired infections, but both types of staph are common inside and outside of hospitals. 

Hospital patients are more likely than the average person to be colonized with MRSA. While two percent of the general population is colonized with MRSA, approximately five percent of U.S. hospitals patients carry MRSA in their nose or on their skin, according to CDC estimates

Not only are hospital patients more likely to be exposed to staph, they are often more vulnerable to infection because they have a deep wound, surgical site, or medical device (e.g., IV, pacemaker, or ventilator) inserted in the body. Hospital patients are also more likely to have a chronic disease that puts them at greater risk for infection — such as diabetes, cancer, HIV, heart or vascular disease, or lung disease.

In hospitals, staph can be transmitted by colonized people in close quarters and contaminated surfaces, including healthcare workers’ hands. However, autoinfection is often the greatest threat. DNA tests of MRSA-infected wounds reveal that 80 percent contain bacteria from the person’s own nasal passages.

Outside of hospitals (i.e., in the community), risk factors for staph infection include uncovered or draining wounds, contact sports, crowded living situations (including nursing homes or prisons), sharing personal items such as razors or towels, and injected drug use.

MRSA vs MSSA Infection: How to Tell the Difference

Wherever or however it’s transmitted, staph bacteria (MSSA or MRSA) can cause a wide range of infections, including:

    • Skin infections: boils, cellulitis, necrotizing fasciitis 
    • Pneumonia
    • Bacteremia/endocarditis
    • Meningitis
    • Osteomyelitis 
    • Septic arthritis
    • Pyomyositis
    • Medical device infections
    • Surgical site infections

Staph infection symptoms vary depending on the part of the body that is affected. Blood tests are required to diagnose staph infection and determine whether it’s MSSA vs MRSA, or another type of bacteria altogether.

Staph infection on the skin usually appears as a painful bump or red, swollen area that’s warm to the touch, pus-filled, and often accompanied by fever.

Cost of Treatment: MSSA vs MRSA

For hospital patients with staph infection, the costs can be steep, depending on the severity and location of the infection. On average, the length of stay and price of treatment associated with MRSA are twice as high as other hospital stays, according to the Healthcare Cost and Utilization Project

Historically, MRSA has been more costly to treat than MSSA, but according to a large 2019 study, that’s no longer the case. Researchers from Johns Hopkins University, the Center for Disease Dynamics, Economics & Policy, and University of Texas Southwestern Medical Center found that MSSA is just as expensive to treat and often more expensive. For example, in 2014, the estimated cost for MSSA-related pneumonia was $40,725, versus $38,561 for MRSA-related pneumonia. For other hospitalizations related to staph, the average price tag was $15,578 for MSSA and $14,792 for MRSA.

Prevention Strategies: MSSA vs MRSA

Healthcare providers have made great strides at reducing the risks of MRSA, but most hospitals still have work to do. With MSSA infection rates on the rise in communities, hospitals will likely be treating more infected or colonized patients, who could transmit the bacteria to other patients during a time when they’re already at high risk for infection. This underscores the need for healthcare providers to remain vigilant about both staph prevention and patient education.

To help reduce the spread of staph in communities, doctors should talk to their patients about effective infection prevention strategies, especially after surgery and before hospital discharge. According to the CDC, these tactics include: 

  • proper and frequent handwashing
  • keeping wounds clean and covered
  • not sharing items that touch or pierce skin, such as towels, razors, or needles

The CDC also advises healthcare organizations to continue making staph prevention a top priority by “implementing CDC recommendations, including the use of Contact Precautions (gloves and gowns), continually reviewing their facility infection data available from CDC’s National Healthcare Safety Network (NHSN), and considering other interventions … such as screening patients at high risk, or decolonization [during] high risk periods.”

Decolonization involves the use of CHG bathing or skin wipes, and a nasal antibiotic (e.g., mupirocin) or antiseptic (e.g., Nozin® Nasal Sanitizer® antiseptic). Unlike nasal antibiotic ointments, antiseptics don’t run the risk of becoming staph-resistant. Furthermore, antiseptics are effective almost immediately as opposed to antibiotics taking up to 5 days for nasal decolonization.

Other healthcare research organizations agree with the CDC’s recommendation to decolonize high-risk patients. Both the Society for Healthcare Epidemiology of America and Health Research and Educational Trust have published similar guidelines. However, recent research suggests decolonization could play an even greater role in reducing MRSA and MSSA infections, especially in intensive care units where patients are most vulnerable. For instance, in a study of 43 hospitals and 74 ICUs, researchers from the University of California Irvine discovered that universal decolonization was more effective at preventing MRSA infections than targeted decolonization or using contact precautions for known staph carriers.


With MSSA on the rise and antibiotic resistance becoming an increasingly serious threat worldwide, the CDC, WHO, and other global health organizations continue to study further prevention methods and treatment strategies. Additionally, it is of critical importance for healthcare providers to stay up to date on staph infection best practices, and to keep personnel and patients educated about their role in preventing the spread of MRSA and MSSA.



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