Infectious arthritis, also called septic arthritis, involves a sudden, severe infection of a joint. It is a type of inflammatory arthritis that can cause swelling, pain, and tissue damage.

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Infectious arthritis usually affects just one joint, but it can spread. As a result, it is essential to diagnose and treat it quickly to prevent severe joint damage and the spread of infection.

This article looks at the symptoms, causes, treatments, and recovery process. It also describes how infectious arthritis differs from reactive arthritis.

Infectious arthritis occurs when bacteria, fungi, or a virus infects a joint, causing inflammation. It can occur suddenly and cause intense pain, fever, and chills.

A person’s immune system regularly removes these harmful pathogens from the body, but when they enter closed areas, such as a joint, they can multiply rapidly and cause severe inflammation and tissue destruction.

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Medical Illustration by Bailey Mariner

Prevalence and impact

Though the name may be misleading, infectious arthritis is not contagious. However, it can be quite serious.

Research shows that illness from septic arthritis occurs in at least one-third of people with the condition. Approximately 7–15% of people hospitalized with the condition will die.

The condition primarily impacts the elderly and young children. People who have artificial joints, or people with underlying medical issues that can weaken their immune systems, are also more susceptible to the condition. This includes people with diabetes and people taking immuno-suppressing medications, for example.

Infectious arthritis can impact people from historically marginalized groups more severely, likely a result of disparities in access to and quality of medical care.

For example, research shows that people of historically marginalized groups are more at risk of developing diabetes than people who are white. Meanwhile, other research shows that for Hispanic Americans and non-Hispanic Black people, musculoskeletal infections like septic arthritis are more likely to lead to amputation of the affected limb.

The most common cause of septic arthritis or infectious arthritis is bacteria, fungi, or viral bodies that enter the space around a joint.

Bacterial infection is the most common cause of septic arthritis. A 2019 review found that bacteria from the Staphylococci family cause more than half of septic arthritis cases. This strain of bacteria also leads to many skin issues.

Other causes of septic arthritis include strains of Streptococci bacteria, which also lead to strep infections, and Neisseria gonorrhoeae bacteria, which can cause gonorrhea.

The bacteria typically reach the joint through the bloodstream.

Undergoing joint replacement surgery or having animal bites, cuts, or puncture wounds on the joints can increase a person’s risk of developing an infection, which could cause septic arthritis.

Having a weakened immune system or a history of other joint problems, such as gout, rheumatoid arthritis, lupus, or osteoarthritis, may also increase the risk as joints that are damaged may be more susceptible to infection.

Septic arthritis causes severe inflammation that can break down tissue in the joint. This may lead to permanent damage to the cartilage and bone.

Like other forms of arthritis, the primary symptoms are swelling, pain, and stiffness in the affected joint. Other septic arthritis signs and symptoms include:

  • pain that is more severe than the pain of noninfectious inflammatory arthritis
  • a limited range of motion in the affected joint
  • redness around the affected joint
  • fever
  • fatigue
  • weakness
  • changes in appetite
  • increased irritability
  • skin rashes

This condition can affect several joints, though septic arthritis in the knee is most common.

Septic arthritis may affect other joints, including:

  • shoulder
  • wrist
  • hip
  • elbow

Symptoms can appear and become severe very soon after the infection develops, sometimes within a few hours. People may also experience other symptoms, depending on the cause of the infection.

Anyone can have infectious arthritis, but certain factors increase the risk, including:

  • existing joint disease, such as rheumatoid arthritis, gout, lupus, or osteoarthritis
  • joint damage
  • recent joint surgery
  • skin infections
  • intravenous (IV) drug use
  • puncture wounds
  • prolonged antibiotic therapy

In addition, anyone who is at risk of contracting bacteria into the joint is at a higher risk of getting the condition. This includes people who have animal bites in the joint, people who have artificial joints, or people undergoing surgery on the joints.

Septic arthritis treatment options can vary depending on which pathogen is causing the condition.

Antibiotics

Because the condition can become severe rapidly, doctors prescribe antibiotics as soon as they suspect infectious arthritis. This may be before joint fluid testing can identify the specific pathogen involved in the infection.

In the first stage of treatment for a bacterial infection, healthcare professionals typically administer antibiotics directly into a person’s bloodstream.

If the antibiotics are effective, the symptoms can improve within 48 hours. However, a person may need IV antibiotics for 2–4 weeks, depending on the severity of the condition. Usually, doctors arrange for people to have IV antibiotics at home.

They may then prescribe oral antibiotics for a further 2–6 weeks.

Learn more about antibiotics here.

Antifungal medications

If a type of fungus is causing the infection, doctors treat it with an antifungal medication instead of antibiotics.

Antiviral medications

Most viral causes of arthritis are self-limiting, meaning that the condition resolves over time. However, doctors may use antiviral medications in some cases, such as in certain instances when the hepatitis C virus is involved.

Draining the joint

Doctors may need to drain fluid from an affected joint to help remove the harmful pathogens and inflammatory substances from the body. They can do this with a syringe or with a procedure called arthroscopy. This involves inserting a small drainage tube into the affected joint through a small incision.

Exercises

People with infectious arthritis may have physical therapy to help reduce symptoms and preserve the joint’s range of motion and function. A doctor may also recommend wearing a splint to support the affected joint.

For anyone wearing a splint, it is essential to do range-of-motion exercises to prevent the joint muscles from shortening. A person should also not wear the splint continuously.

If a person does not receive early, robust treatment, infectious arthritis may cause permanent damage to the tissues and bones in the joint.

The effects of this damage on daily life depend on which joint is involved. For example, damage to a knee joint can affect the ability to stand or walk.

Infectious arthritis may also occur alongside osteomyelitis, which is an infection within a bone.

It is important to have infectious arthritis diagnosed as soon as possible. First, a doctor performs a physical examination and discusses the person’s medical history with them.

This alone does not provide enough information for a doctor to distinguish infectious arthritis from many other inflammatory conditions, so if they suspect infectious arthritis, they will recommend further tests.

These tests may require samples of blood and fluid from the affected joint. A 2018 clinical review heralded joint fluid analysis as the diagnostic gold standard for infectious arthritis.

Doctors may also recommend imaging tests, such as X-rays or MRI scans, to assess the extent of damage that the infection has already caused.

A person may mistake infectious arthritis for reactive arthritis. The two can cause similar symptoms. However, infectious arthritis results from an active infection in the joint, while reactive arthritis usually results from a recent infection elsewhere in the body.

Some people may develop reactive arthritis following a sexually transmitted infection or an infection of the gastrointestinal tract from food poisoning.

Reactive arthritis does not typically result from an infection spreading into a joint. Instead, it occurs when the immune system overreacts to the initial infection, triggering joint inflammation.

Infectious arthritis is a severe condition that can cause permanent bone and tissue damage. Bacterial infections are the most common cause, although viral and fungal infections can also be responsible.

A person with infectious arthritis may experience sudden swelling, severe pain, dizziness, and fatigue.

Early and aggressive treatment, including IV antibiotics, can significantly improve a person’s septic arthritis outlook. If treatment begins in time, a person may make a full recovery without any lasting damage.

Can septic arthritis spread to other joints?

Infectious arthritis usually affects only one joint. However, it can affect multiple joints in some cases and may spread to other parts of the body if left untreated.

What other organisms can cause septic arthritis?

Although bacteria usually cause septic arthritis, several types of viruses and fungi can also cause an infection.

Rubella, hepatitis B or C, parvovirus, alphavirus, and flavivirus may cause viral arthritis. Certain types of fungi, including Candida albicans, may also cause septic arthritis, but this is very rare.

When does a person need surgery for septic arthritis?

Treatment for infectious arthritis often involves a combination of antibiotics and joint fluid drainage using either a tube or syringe.

In some cases, a doctor may also recommend surgery to drain the joint, although this can depend on the severity of infection, the specific joint that the arthritis is affecting, and whether or not other treatments are effective.