Overview

MRSA is a type of Staphylococcus aureus (“staph”) bacteria that has become resistant to many commonly used antibiotics, including methicillin and amoxicillin. Staph bacteria are normally found on the skin or in the nose of about 30% of healthy people without causing harm (called colonization).

An infection occurs when the bacteria enter the body through a break in the skin. Because MRSA is resistant to many antibiotics, including penicillin, methicillin, and cephalosporins. Infections can be harder to treat and may require specific antibiotics, sometimes given intravenously.

Most infections start on the skin, appearing as a painful, swollen, red bump or boil that often resembles a spider bite. If untreated, the infection can spread deeper and cause fever, chills, bloodstream infection (sepsis), pneumonia, or bone/joint infections.

How common is it?

• Approximately 1–2% of the population carries MRSA in their nose or on their skin without symptoms (colonization).
• Each year, about 275,000–320,000 people in the U.S. are hospitalized with MRSA infections.
• MRSA accounts for roughly 30–50% of hospital-acquired Staph infections and is a leading cause of skin and soft-tissue infections in emergency departments.

In 2017, MRSA was responsible for approximately 119,000 bloodstream infections and nearly 20,000 deaths in the U.S.. Worldwide, the proportion of staph infections that are MRSA ranges from >1% to <50% depending on the country and setting.

Types

MRSA infections are classified by where and how the bacteria were acquired:

Healthcare-Associated MRSA (HA-MRSA)

This type of MRSA is acquired in healthcare settings, such as hospitals, nursing homes, and dialysis centers.

• Patients are more vulnerable because they may have compromised skin (due to surgery or wounds), lower immune strength, or medical devices (like IVs or catheters).
• ITend to be more serious because the bacteria often spread where the skin is already compromised.
• More likely to cause severe issues like pneumonia, bloodstream infections (sepsis), or surgical wound infections.

Community-Associated MRSA (CA-MRSA)

Emerged in the late 1990s–early 2000s, this type affects people who have not been recently hospitalized or had a medical procedure.

• Spreads among healthy individuals through close contact or shared items in gyms, schools, athletic programs, and dormitories.
• Often begins as a skin infection, appearing as a painful, red bump or abscess (boil).
• Spread through direct contact with an infected wound or by touching items (towels, razors, equipment) contaminated with the bacteria.

Symptoms

The appearance of an MRSA infection depends on whether it is limited to the skin or has spread deeper into the body.

Skin and soft-tissue infections (most common – ~75–90% of cases)

• Red, swollen, painful bumps that may look like pimples or spider bites
• Warm to the touch, often filled with pus or drainage
• May develop blisters or abscesses; sometimes confused with cellulitis
• Usually appears on areas with hair or friction (buttocks, armpits, groin, neck) or where skin is broken
• Fever may accompany the infection

Signs of more serious or invasive infection (seek immediate medical care)

• Bloodstream infections (bacteremia): fever, chills, rapid spread of redness, severe pain, weakness, or confusion
• Pneumonia: cough, shortness of breath, chest pain, fever, chills
• Other severe manifestations: chest discomfort, lightheadedness, or sudden changes in mental status

Early recognition and proper treatment significantly reduce the risk of complications. Most uncomplicated skin infections can be treated with incision and drainage plus appropriate antibiotics; severe cases may require hospitalization and intravenous therapy.

Causes

MRSA begins as a regular staph bacterium that has developed the ability to resist certain antibiotics. The bacteria accomplish this by altering their internal proteins so that the antibiotics can no longer attach and stop them from multiplying. Overuse and misuse of antibiotics worldwide have driven the selection and spread of these resistant strains.

Risk factors for acquiring or developing MRSA infection

Not all individuals are equally susceptible to MRSA. Risk increases when the bacteria gain entry or evade the immune system. Key factors include:

Skin barrier breakdown

• Chronic skin conditions (eczema, psoriasis)
• Shaving, waxing, or repeated friction (e.g., “turf burns” in athletes)
• Sharing items like towels, razors, or sports gear

Close-contact settings (favor person-to-person transmission)

• Living in crowded spaces (dorms, shelters, military housing)
• Gyms, locker rooms, and shared sports equipment
• Sharing household items or participating in contact sports

Healthcare-related exposures

• Recent hospitalization or surgery (especially >3 months)
• Surgical wounds or catheter use
• Dialysis treatment or IV lines

Medical and health conditions

• Previous MRSA infection or known colonization
• Recent antibiotic use (especially broad-spectrum or multiple courses)
• Diabetes or slow-healing woulds
• Chronic lung disease or obesity

Diagnosis

To confirm an MRSA infection, healthcare providers collect a sample from the infected area and send it to a lab to see if the bacteria grow. This process, called a bacterial culture, helps confirm both the presence of staph and its antibiotic resistance.

Culture Testing (The Gold Standard)

• A sample is collected from the suspected site of infection. This may involve swabbing:
  • A wound, abscess, or area of skin containing pus
  • Sputum (for a suspected lung infection/pneumonia)
  • Urine or blood (for deeper or systemic infections)
• The sample is sent to a lab to determine if staph bacteria grow and, if so, whether that specific strain is resistant to methicillin and other common antibiotics (confirming MRSA).

Colonization Screening

A nasal swap is commonly used to check if a person is merely colonized (carrying the bacteria without symptoms) to prevent potential spread, especially in healthcare settings.

Imaging (when invasive infection is suspected)

In some cases, X-rays or CT scans help determine whether the infection has spread to deeper tissues or organs. Imaging tests do not diagnose MRSA, but they show the extent of the infection and damage to help guide treatment decisions.

Treatment

While MRSA is resistant to many common antibiotics (e.g., penicillin, amoxicillin, cephalexin), several effective drugs remain available. Choice depends on infection site, severity, patient allergies, and local resistance patterns.

Commonly effective antibiotics

• Vancomycin – often first-line for serious infections
• Linezolid
• Daptomycin
• Clindamycin
• Trimethoprim-sulfamethoxazole (Bactrim)
• Doxycycline
• Ceftaroline (a newer cephalosporin effective against MRSA)

Treatment approaches

• Uncomplicated skin and soft-tissue infections (most common):
  • Incision and drainage of abscesses/boils (often the most important step)
  • Oral antibiotics (e.g., Bactrim, doxycycline, clindamycin, linezolid) for 5–10 days
• Moderate to severe or invasive infections (pneumonia, bacteremia, osteomyelitis, endocarditis):
  • Hospitalization and prolonged IV therapy (vancomycin, daptomycin, or linezolid) for 2–6 weeks or longer
  • DWound care, elevation, and warm compresses are essential for skin infections.

Most patients respond well when treatment is started promptly and the correct antibiotic is chosen based on culture results.

Complications

If MRSA is not treated early or spreads beyond the skin, serious and sometimes life-threatening complications can occur:

• Abscesses in deeper tissues
• Bloodstream infection (bacteremia)
• Bone or joint infections (osteomyelitis, septic arthritis)
• Pneumonia
• Heart valve infection (endocarditis)
• Organ damage
• Sepsis – a life-threatening systemic response

Why complications occur: Delayed or ineffective treatment allows bacteria to move from localized skin sites into the bloodstream or organs.

Prevention

MRSA is preventable in most cases through basic hygiene and common-sense measures.

• Wash hands frequently with soap and water for at least 20 seconds, especially after the gym or using public spaces.
• Always keep cuts, scrapes, and abrasions covered with clean, dry bandages until they are healed.
• Avoid sharing personal items that touch the skin, like razors, towels, washcloths, or athletic gear.
• Clean and disinfect frequently touched surfaces, especially athletic equipment and high-touch areas in your home (door handles, bathroom).

The Bottom Line

MRSA is common, but it’s not a death sentence. Most cases are straightforward skin infections that heal quickly with proper care. Good hygiene, quick attention to suspicious skin bumps, and finishing prescribed antibiotics are your best tools.