Septic arthritis typically causes extreme discomfort and difficulty using the affected joint. The joint could be swollen, red and warm, and you might have a fever.

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.

Septic arthritis can develop when an infection, such as a skin infection or urinary tract infection, spreads through your bloodstream to a joint. Less commonly, a puncture wound, drug injection, or surgery in or near a joint can give the germs entry into the joint space.

The lining of your joints (synovium) has little ability to protect itself from infection. Your body's reaction to the infection — including inflammation that can increase pressure and reduce blood flow within the joint — contributes to the damage.

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 wounds 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.

If treatment is delayed, septic arthritis can lead to joint degeneration and permanent damage.