The most common causes of septic arthritis are certain bacterial infections that start in other areas of the body and spread to the joints. However, fungal infections, mycobacteria, and viruses may also cause septic arthritis.

Septic arthritis, or infectious arthritis, occurs when bacteria or other microorganisms enter into a joint and cause swelling, pain, and stiffness, similar to other types of arthritis. Unlike other types of arthritis, these infections often appear in a single joint. They may also cause fever, warmth in the joint, and a reluctance or refusal to move the affected joint.

The condition affects about 2–6 out of every 100,000 people. While it can affect both children and adults, it is more common in children.

For adults, some risk factors for developing septic arthritis may include being over the age of 80, living with diabetes, recently experiencing surgery, and living with rheumatoid arthritis.

This article reviews bacterial infections that may cause septic arthritis, including the most common type. It also explores fungal infections that may cause septic arthritis, its underlying causes, possible symptoms, treatment, and when to speak with a doctor.

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Staphylococcus aureus infection is the most common cause of septic arthritis in both children and adults. Other bacteria can also cause septic arthritis, including:

In most people, the condition does not start in the joint. Instead, the bacteria spreads to the joints from infections in other areas of the body, via the bloodstream.

Other potential bacterial infections that may lead to septic arthritis include:

Learn more about the symptoms of a bacterial infection here.

Fungal infections are a less common cause of septic arthritis. When a fungal infection is responsible for septic arthritis, the infection may be harder to diagnose and treat.

Similarly, viral infections, and infections resulting from other pathogens, may also cause septic arthritis.

Often, septic arthritis develops due to the presence of an infection in another area of the body, but it can occur anytime bacteria or another pathogen gets into a joint.

Some possible underlying causes of infections in the joints include:

  • a recent injury
  • recent surgery on a joint
  • injections

Potential risk factors for developing an infection can include living with a long-term health condition, such as diabetes, kidney failure, or rheumatoid arthritis. Additionally, individuals with a weakened immune system due to conditions, including cancer and HIV, or from taking immunosuppressant medications, are also at a higher risk.

These conditions do not cause septic arthritis directly, but they can make it possible for pathogens to get into the joint and cause the condition.

Septic arthritis can cause several symptoms similar to other forms of arthritis. They often appear rapidly but can have a slower onset, depending on the pathogen. Common symptoms that may present as septic arthritis develops include:

Typically, septic arthritis affects the knee, but it can affect the wrists, hips, or ankles. Rarely, it may affect more than one joint.

If a person leaves septic arthritis untreated, it may lead to permanent joint damage. In severe instances, it can be fatal.

Treatment for septic arthritis will vary depending on the exact underlying cause.

Most often, septic arthritis is the result of bacterial infections, so a doctor will likely prescribe antibiotics to kill the bacteria. A healthcare professional may administer this medication intravenously (through the veins) or orally.

Another treatment method involves a doctor draining the joint, which may help:

  • remove infected synovial fluid, which typically lubricates certain types of joints
  • relieve pain
  • reduce inflammation
  • prevent further damage to the joint

Following drainage, a doctor may recommend a person not move the joint for 2–3 days. Following this, a person will likely need physical therapy to help restore joint mobility and strength. Some people may require a consultation with an orthopedic surgeon to see if they require surgery.

A parent or guardian should consider taking their child to a doctor if they are experiencing joint pain or show a reluctance to move a joint. This could be a sign of injury, septic arthritis, or another issue.

Adults who have had recent surgery, present with other symptoms, or have risk factors for developing septic arthritis, should see a doctor if they develop joint pain. Early diagnosis and treatment can help prevent complications from occurring.

Risk factors include:

  • being over the age of 80
  • living with diabetes, rheumatoid arthritis, or osteoarthritis
  • recent joint surgery
  • being sexually active
  • living with HIV
  • having a skin infection
  • intravenous drug use
  • puncture wounds near a joint

Septic arthritis typically occurs when a bacterial infection from another area of the body moves into a joint. It often presents with symptoms quickly, causing swelling and pain in the affected joint.

Though bacterial infections are often the cause, fungal infections may also cause it to develop.

A person may develop septic arthritis following surgery, injury, or a pathogen spreading from another site of infection to the joint via the bloodstream. Other factors, such as advanced age, living with certain health conditions, and sexual activity, may also increase the risk of developing septic arthritis.

A person should seek medical advice as soon as possible if they develop sudden joint pain or other symptoms of septic arthritis. Treatment often consists of an antibiotic regimen and draining the joint. A person will also likely need physical therapy following joint drainage.