Understanding MRSA Infection

Medically Reviewed by Stephanie S. Gardner, MD on April 30, 2023
4 min read

Methicillin-resistant Staphylococcus aureus (MRSA) is a bacteria that causes infections in different parts of the body. It's tougher to treat than most strains of staphylococcus aureus – or staph – because it's resistant to some commonly used antibiotics.

Though most MRSA infections aren't serious, some can be life-threatening. Many public health experts are alarmed by the spread of tough strains of MRSA. It’s sometimes called a "superbug" because it's hard to treat.


The symptoms of MRSA infection depend on where you've been infected.

MRSA most often appears as a skin infection, like a boil or abscess. It also might infect a surgical wound. In either case, the area would be:

  • Swollen
  • Red
  • Painful
  • Filled with pus
  • Have yellow crusting

Many people who have a staph skin infection often mistake it for a spider bite.

If staph infects the lungs and causes pneumonia, you will have:

  • Shortness of breath
  • Fever
  • Chills

MRSA can cause many other symptoms because once it gets into your bloodstream, it can settle anywhere. MRSA can cause an abscess (inflamed tissue with pus inside) in your spleen, kidney, or spine. It can cause endocarditis (heart valve infections), osteomyelitis (bone infections),  joint infections, mastitis (infection in the breast), and infections of implanted prosthetic devices (like those used in a knee replacement, for instance). Unlike most MRSA skin infections, which can be treated in the doctor's office, these more serious infections will land you in the hospital. You’ll get antibiotics in an IV to help kill the infection.

Very rarely, staph can result in necrotizing fasciitis, or "flesh-eating" bacterial infections. These are serious skin infections that spread very quickly. While frightening, very few necrotizing fasciitis cases have been reported.


Garden-variety staph are common bacteria that can live in our bodies. Plenty of healthy people carry staph without being infected by it. In fact, one-third of everybody has staph bacteria in their noses.

But staph can be a problem if it manages to get into the body, often through a cut. Staph is one of the most common causes of skin infections in the U.S. Usually, these are minor and don't need special treatment. Less often, staph can cause serious problems like infected wounds or pneumonia.


Staph can usually be treated with antibiotics. But over the decades, some strains of staph, like MRSA, have become resistant to antibiotics that once destroyed them. MRSA was discovered in 1961. It's now resistant to amoxicillin, methicillin, oxacillin, penicillin, and other common antibiotics known as cephalosporins.

While some antibiotics still work, MRSA is constantly adapting. Researchers developing new antibiotics are having a tough time keeping up.

Another type of staph, MSSA (methicillin-sensitive Staphylococcus aureus), is very common. The main difference between MSSA and MRSA is that MSSA is much less resistant to the antibiotics most doctors will give you. It can cause infections, though, if it gets into the body. 

MRSA is spread by contact. You could get MRSA by touching another person who has it on their skin. Or you could get it by touching things that have the bacteria on them. MRSA is carried by about 2% of the population (or 2 in 100 people), although most of them aren't infected.

There are two types of people who get MRSA.  One is in decline: those who get it in hospitals or other health care places. The other is on the rise: those who get it in the community. 

MRSA infections are common among people who have weak immune systems who are in hospitals, nursing homes, and other health care centers. Infections can appear around surgical wounds or invasive devices, like catheters or implanted feeding tubes. 

The Department of Health and Human Services reviews the  National Action Plan to Prevent Health Care-Associated Infections regularly. Recent studies suggest that implementing existing prevention practices can lead to up to a 70 percent reduction in certain infections.

Alarmingly, MRSA is also showing up in healthy people who have not been hospitalized. This type of MRSA is called community-associated MRSA, or CA-MRSA. 

CA-MRSA skin infections have been identified among some people who share close quarters or have more skin-to-skin contact. Examples are team athletes, military recruits, prison inmates, and children in day care. But more and more CA-MRSA infections are being seen in the general community, especially in certain geographic regions.

CA-MRSA is also more likely to affect younger people. In a study of Minnesotans published in The Journal of the American Medical Association, the average age of people with MRSA in a hospital or health care facility was 68. But the average age of a person with CA-MRSA was only 23.

In most cases, MRSA is easily treated. But MRSA infections can be serious, so make sure you get medical care. You should call your doctor if you notice signs of active infection – most likely of the skin – with a spreading, painful, red rash or abscess. 

If you are already being treated for an infection, watch for signs your medicine isn't working. Those may include:

  • The infection is no better after you’ve been taking the antibiotic 3 or 4 days.
  • The rash spreads.
  • You get a fever, or your fever gets worse.

People who are sick or have weak immune systems have a higher risk of getting serious MRSA infections. If you have a condition that lowers your immunity, call your doctor right away if you think that you might have an infection.