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One of the subtypes of arthritis, a disease characterized by inflammation of joints, is infectious (septic) arthritis. This article describes risk factors, symptoms, diagnosis and treatment of infectious arthritis.

Arthritis, a disease described as inflammation of joints, is a painful and debilitating disorder that leads to joint stiffness and pain.

There are more than a 100 different forms of arthritis, the major categories of which include degenerative arthritis (osteoarthritis), inflammatory arthritis, infectious (septic) arthritis and metabolic arthritis.

Infectious arthritis develops due to an infection in a joint, which occurs when a microorganism (such as a bacteria or virus) spreads to either a joint or the fluid that surrounds the joint (known as synovial fluid). Generally, the infection starts in a different part of the body but then spreads through the bloodstream and into the surrounding joint tissue. The microorganism can enter the body through either surgery, an open wound, or injections (shared needles).

Generally, infectious arthritis is limited to only one joint, though it tends to affects larger joints such as knee, hip, or shoulder.

1. Infectious arthritis: Risk factors

There are certain risk factors that predispose individuals to developing infectious arthritis, including:

  • Age, as infectious arthritis more commonly occurs in children and older patients
  • Use of illegal drugs
  • Prior joint problems such as arthritis, gout, or lupus
  • History of joint surgery
  • Abusing alcohol
  • Having an open wound
  • Having specific skin conditions
  • Taking medicines that suppress the immune system (immunosuppressants)
  • Weakened immune system
  • Having cancer
  • Smoking
  • Having diabetes

2. What are the symptoms of infectious arthritis?

Not all patients with infectious arthritis will experience the same set of symptoms, and these symptoms will vary depending on the age of the patient and the medications they are taking. These are the common symptoms that can be experienced by patients with infectious arthritis:

  • Significant pain, which worsens when you move
  • Joint swelling
  • Warmth and redness around joint
  • Fever and chills
  • Excess fatigue
  • Feeling weak
  • Reduced appetite
  • High heart rate
  • Feeling irritable

3. Diagnosis: How do doctors diagnose infectious arthritis?

If your doctor suspects that you may have infectious arthritis, then he or she will examine your joints, ask questions related to the symptoms and order tests that can confirm the presence of infectious arthritis.

The type of test that is most commonly conducted in order to diagnose infectious arthritis is called arthrocentesis, which involves inserting a needle into the painful joint and taking a sample of synovial fluid. Then, the sample is sent to a lab that will look for presence of white blood cells and bacteria. Results from this test can determine whether there is an infection in the joint and what types of microorganism is causing the infection.

In such a case, the doctor may also ask for a blood sample to see if the bacteria are also present in the blood stream. Results from this can be used to determine how severe the infection is.

Imaging tests, such as those conducted using x-rays, MRI scans, CT scans, and nuclear scans, can be used to both confirm the presence of infection as well as evaluate the extent of the damage to your joints caused by the infection.

4. Treatment of infectious arthritis 

Unlike other types of arthritis, infectious arthritis is very treatable if caught early on and treated aggressively. As infectious arthritis is usually caused by a bacterial infection, the doctor will likely begin with a course of antibiotics to kill the bacteria causing the infection. Different types of bacteria require different antibiotics and therefore the doctor will pick the appropriate antibiotic depending on which specific bacterial species is causing the infection.

Infectious arthritis needs to be treated as quickly and aggressively as possible. If left untreated, it can cause osteoarthritis and severe damage to the joint. Therefore, the doctor will order intravenous antibiotics, which are given through the veins, as opposed to taking them orally (through your mouth). Patients will generally start to feel better within 48 hours of first antibiotic treatment.

If the infection is not too severe, then the doctor may order oral antibiotics, which will need to be taken for six to eight weeks. If the infection is caused by a fungus instead of bacteria, then the doctor will prescribe antifungal medication. Finally, if Infectious arthritis is caused by a virus, then that does not require any medication.

In many cases, patients with infectious arthritis need to have their synovial fluid drained as it is infected. In most cases, this is done through a surgery or open procedure to wash the joint.  Synovial fluid is generally drained using:

  • Arthroscopy, which is an open surgical procedure
  • Or arthrocentesis, which involves inserting a small needle to remove infected fluid without surgery

During arthroscopy, the doctor will make small incisions near the affected joint and then insert a small tube with a camera into the incision. Using the camera image, the doctor will suction the infected fluid from the joint. Commonly, a drain or tube will be inserted and left in the joint to stop the swelling. The drain is then removed after a few days.

In some cases, another surgery is required to actually take out damaged sections of the joint or replace the joint, but only after the infection has been fully treated and removed.

Other treatments are used to reduce pain, and can be used alongside the antibiotic treatment, including:

  • Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin
  • Resting the joint
  • Splinting the joint
  • Physical therapy to regain range of movement

  • Smith, James W., and Elizabeth A. Piercy. "Infectious arthritis." Clinical infectious diseases (1995): 225-230.
  • Sharp, John T., et al. "Infectious arthritis." Archives of Internal Medicine 139.10 (1979): 1125-1130.
  • Tarkowski, Andrej. "Infectious arthritis." Best practice & research Clinical rheumatology 20.6 (2006): 1029-1044.
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