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Bacterial Arthritis (Septic Arthritis) - Definition, Symptoms, Causes, Risk Factors


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Definition|
Septic arthritis is inflammation of a joint caused by a bacterial infection. It's also known as infectious or bacterial arthritis.
Septic, or infectious, arthritis is infection of one or more joints by microorganisms. Normally, the joint is lubricated with a small amount of fluid that is referred to as synovial fluid or joint fluid. The normal joint fluid is sterile and, if removed and cultured in the laboratory, no microbes will be detected. With this form of arthritis, microbes are identifiable in an affected joint's fluid. Infants and older adults are most likely to develop septic arthritis.
Most commonly, septic arthritis affects a single joint, but occasionally more joints are involved. The joints affected vary somewhat depending on the microbe causing the infection and the predisposing risk factors of the patient affected. Septic arthritis is also called infectious arthritis.
Symptoms|
Septic arthritis typically causes severe pain, swelling, redness and heat in affected joints. These symptoms tend to develop quickly over a few hours or days.
Joints most commonly involved are large joints, such as the knees, ankles, hips, and elbows. In patients with risk factors for joint infection, unusual joints can be infected, including the joint where the collarbone (clavicle) meets the breastbone (sternum). With uncommon microbes, such as Brucella spp., atypical joints can be infected, such as the sacroiliac joints.
Causes|
Septic arthritis can be caused by bacterial, viral or fungal infections. Bacterial infection with Staphylococcus aureus (staph) is the most common cause. Staph commonly lives on even healthy skin.
The most common causes of septic arthritis are bacterial, including Staphylococcus aureus and Haemophilus influenzae. In certain "high-risk" individuals, other bacteria may cause septic arthritis, such as E. coli and Pseudomonas spp. in intravenous drug abusers and the elderly, Neisseria gonorrhoeae in sexually active young adults, and Salmonella spp. in young children or in people with sickle cell disease. Other bacteria that can cause septic arthritis include Mycobacterium tuberculosis and the spirochete bacterium that causes Lyme disease.
Viruses that can cause septic arthritis include hepatitis A, B, and C, parvovirus B19, herpes viruses, HIV (AIDS virus), HTLV-1, adenovirus, Coxsackieviruses, mumps, and Ebola. Fungi that can cause septic arthritis include Histoplasma, Coccidioides, and Blastomyces.
Septic arthritis is not contagious. However, many of the microbes that cause septic arthritis can be transmitted from an infected patient to another, including Neisseria gonorrhoeae, Mycobacterium tuberculosis, and HIV
Risk Factors|
While joint infection occasionally affects people with no known predisposing risk factors, it more commonly occurs when certain risk situations are present.
Risk factors for septic arthritis include:
Existing joint problems. Chronic diseases and conditions that affect your joints — such as osteoarthritis, gout, rheumatoid arthritis or lupus — can increase your risk of septic arthritis, as can an artificial joint, previous joint surgery and joint injury.
Taking medications for rheumatoid arthritis. People with rheumatoid arthritis have a further increase in risk because of medications they take that can suppress the immune system, making infections more likely to occur. Diagnosing septic arthritis in people with rheumatoid arthritis is difficult because many of the signs and symptoms are similar.
Skin fragility. Skin that breaks easily and heals poorly can give bacteria access to your body. Skin conditions such as psoriasis and eczema increase your risk of septic arthritis, as do infected skin wounds. People who regularly inject drugs also have a higher risk of infection at the site of injection.
Weak immune system. People with a weak immune system are at greater risk of septic arthritis. This includes people with diabetes, kidney and liver problems, and those taking drugs that suppress their immune systems.
Joint trauma. Animal bites, puncture woods or cuts over a joint can put you at risk of septic arthritis.

Having a combination of risk factors puts you at greater risk than having just one risk factor does.

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