Infectious arthritis

by Nathan Wei, MD, FACP, FACR

Nathan Wei is a nationally known board-certified rheumatologist and author of the Second Opinion Arthritis Treatment Kit. It's available exclusively at this website... not available in stores.

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Infectious arthritis means infection of a joint or joints. Infections are most often caused by bacteria, but can also be caused by fungus or yeast. Viral infections can also occur, but this is less common.

Bacteria can enter a joint in several ways. Trauma can introduce bacteria into the joint. This can range from large traumatic injuries to very small injuries, such as punctures by a nail or thorn.

Bacteria can also spread to a joint by traveling through the blood (bacteremia). Small amounts of bacteria can enter the blood during dental procedures such as teeth cleaning or colon procedures. Bacteria frequently enter the blood in patients who have pneumonia or other serious infections. Kidney and bladder infections can cause bacteremia.

Surgical procedures can also create an opportunity for bacteria to enter a joint. This is becoming less common than it used to be with adherence to sterile technique.

About half of the infections that occur following hip and knee replacement occur much later during episodes of bacteremia, where bacteria seed into the area of the joint replacement. As a result, all patients who receive joint replacements are instructed to take preventative antibiotic therapy before and after any dental or surgical procedures which may cause a bacteremia.

Those who are at increased risk for infectious arthritis:

• Patients with chronic rheumatoid arthritis.
• Patients with certain systemic infections, including gonorrhea and HIV infection. • Patients with cancer.
• IV drug abusers and alcoholics.
• Patients with artificial (prosthetic) joints.
• Patients with diabetes, sickle cell anemia, or systemic lupus erythematosus (SLE).
• Patients with recent joint injuries or surgery, or patients receiving medications injected directly into a joint.

Infectious arthritis usually is easily recognized by the presence of a hot, swollen, and painful joint which develops rapidly and without obvious trauma. However, some infections can develop slowly and only cause mild symptoms of swelling and stiffness.

It's important to realize that a hot painful joint is not always infected. Several other conditions can cause these symptoms, including gout, pseudogout, rheumatoid arthritis, fractures, or tumors.

In adults, the infectious organisms include Streptococcus pyogenes and Streptococcus viridans as well as Staphylococcus aureus. Staphylococcus epidermidis is usually involved in joint infections related to surgery. Sexually active adults frequently develop infectious arthritis from Neisseria gonorrhoeae infections. Older adults are often vulnerable to joint infections caused by gram-negative bacilli, such as Salmonella and Pseudomonas.

In most cases the patient will have fever and chills, although the fever may be only low-grade.

Septic arthritis is considered a medical emergency because of the damage it causes to bone as well as cartilage, and its potential for creating septic shock, which can be fatal.

Staphylococcus aureus can destroy cartilage in one or two days. If the infection is caused by bacteria, it can spread to the blood and surrounding tissues, causing abscesses or septicemia (blood poisoning).

The diagnosis of infectious arthritis depends on a combination of laboratory testing with history and physical examination of the affected joint. Infectious arthritis can coexist with other forms of arthritis, gout, rheumatic fever, Lyme disease, or other disorders that can cause a combination of joint pain and fever.

Laboratory testing is necessary to confirm the diagnosis of infectious arthritis. The doctor will perform an arthrocentesis, a procedure that involves withdrawing a sample of synovial fluid from the joint with a needle and syringe.

The fluid sample is sent for culture. Fluid from infected joints is cloudy and watery. Cell counts usually indicate a large number of white cells; a level higher than 100,000 cells/mm3 or a neutrophil proportion greater than 90% suggests septic arthritis. A Gram stain of the culture obtained from the synovial fluid is usually positive for the specific disease organism.

Doctors sometimes order a biopsy of the synovial tissue near the joint if the fluid sample is negative. Cultures of other body fluids, such as urine, blood, or cervical mucus, may be taken in addition to the synovial fluid culture.

Diagnostic imaging is not helpful in the early stages of infectious arthritis. Destruction of bone or cartilage does not appear on x rays until 10-14 days after the onset of symptoms. Imaging studies are sometimes useful if the infection is in a deep-seated joint.

Infectious arthritis requires usually requires several days of treatment in a hospital, with follow-up medication and physical therapy lasting several weeks or months.

After the disease organism has been identified, a drug that targets the specific bacterium or virus is given.

Intravenous antibiotics are administered for about two weeks, or until the infection has disappeared. The patient may then be given a two- to four-week course of oral antibiotics. Physical therapy to encourage range-of-motion is helpful.

In some cases, surgery is necessary to drain fluid from the infected joint. Patients who need surgical drainage include those who have not responded to antibiotic treatment, those with infections of the hip or other joints that are difficult to reach with arthrocentesis, and those with joint infections related to penetrating wounds.

Infectious arthritis often causes intense pain.

The prognosis depends on prompt treatment with antibiotics and drainage of the infected joint. About 70% of patients will recover without permanent joint damage. However, many patients will develop osteoarthritis or deformed joints.

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