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MRSA Infection

Causes and Risk Factors, Signs and Symptoms

Physician-developed and -monitored.

Original Date of Publication: 20 Feb 2008
Reviewed by: Stanley J. Swierzewski, III, M.D.
Last Reviewed: 20 Feb 2008

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Home » MRSA Infection » Causes and Risk Factors, Signs and Symptoms

Causes and Risk Factors

MRSA infection is caused by a type of Staphylococcus aureus bacteria that is resistant to antibiotics used to treat most staph infections. Staphylococcus bacteria live normally on the skin and mucous membranes (e.g., nose) in about 30% of people. When these bacteria enter the body (e.g., through a cut or break in the skin, or a surgical wound), they can cause staph infection.

Patients who have recently been hospitalized (within the past year) and patients in long-term health care facilities, including nursing homes and dialysis centers, are at increased risk for health-care associated MRSA infection. Medical conditions that weaken the immune system (e.g., HIV/AIDS, cancer), recent invasive medical procedures (e.g., surgery, catheterization, dialysis), and recent use of antibiotics also increases the risk for HA-MRSA.

Health care workers (e.g., doctors, nurses, physician assistants) and people who are in close contact with health care workers are at increased risk for developing staph infections, including MRSA. Children also have a higher risk for infection, possibly because their immune systems are not fully developed.

Risk factors for community-associated MRSA infection include participation in contact sports (e.g., wrestling, football), sharing contaminated items (e.g., towels, razors), and poor hygiene. People who are exposed to crowded conditions (e.g., childcare, military barracks, prison) also are at increased risk for CA-MRSA infection.

Skin-to-skin contact, especially if there is a cut, scrape, or other type of break in the skin, increases the risk for MRSA infection. Some types of methicillin-resistant Staphylococcus aureus bacteria live in the anal area and can be passed between sexual partners. Recently, an increase in MRSA infections in men who have sex with men (MSM) has been reported.

It may be possible for people to develop MRSA infections through contact with an infected pet. The bacteria have been found in dogs, cats, rabbits, horses, cows, and pigs. More research is needed to determine if the bacteria can be easily spread in this manner.

Signs and Symptoms

Methicillin-resistant Staphylococcus aureus infections are a serious health concern. Staph infections, including MRSA, often cause painful skin inflammation (i.e., redness, warmth, swelling) and pus-filled, pimple-like lesions on the skin that do not heal as expected (infection of a hair follicle; called folliculitis). Early MRSA infections sometimes are mistaken for insect or spider bites.

Symptoms of severe staph infection include the following:

  • Bone pain
  • Chest pain
  • Chills
  • Drainage of pus
  • Fatigue
  • Fever
  • Headache
  • Joint pain
  • Malaise (generally feeling unwell)
  • Muscle aches
  • Rash
  • Shortness of breath, painful breathing

Complications Because they are resistant to treatment, MRSA infections often cause serious complications and widespread infection. In severe cases, skin infections can result in tissue death (necrosis). Other MRSA complications include the following:

  • Brain or spinal cord abscess (nervous system infections)
  • Cellulitis (connective tissue infection)
  • Endocarditis (infection of the membrane that lines the heart)
  • Organ failure (e.g., kidney)
  • Osteomyelitis (bone marrow infection)
  • Pharyngitis (throat infection)
  • Pneumonia (respiratory infection that affects the lungs)
  • Septic arthritis and septic bursitis (joint infections)
  • Septicemia (also called blood poisoning)
  • Sinusitis (sinus infection)
  • Thrombophlebitis (inflammation of a vein and formation of a blood clot)
  • Toxic shock syndrome (acute infection that involves multiple organ systems)
  • Urinary tract infection (UTI)

MRSA Infection, Causes and Risk Factors, Signs and Symptoms reprinted with permission from
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