Reactive arthritis is typically due to joint inflammation in response to an infection elsewhere in the body. The most common cause of septic arthritis is viral bodies, fungi, or bacteria entering the joint area and causing infection.

While there are key differences in the causes, both conditions can display similar symptoms.

Reactive arthritis is an inflammatory condition that affects the joints, urinary tract, and eyes. A person may develop the condition if an infection triggers the immune system to react with inflammation, causing inflammatory arthritis.

Septic arthritis is a painful infection in the joint that may have spread through the blood from another part of the body to the joint or the fluid surrounding the joint.

The infection can also spread directly to the joint through trauma, surgery, and joint injections. The joint is usually hot and swollen. Symptoms are acute and present for days rather than weeks or months.

This article compares reactive and septic arthritis and discusses their signs and symptoms.

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Design by MNT; Photography by delihayat/Getty Images & athima tongloom/Getty Images

Reactive arthritis and septic arthritis may cause similar symptoms, which may lead a person to mistake one for the other. However, the two have several key differences.

Reactive arthritisSeptic arthritis
CausesThe most common cause is a bacterial infection, usually in the urinary or gastrointestinal tract.

The bacteria may not affect the joint directly but triggers an inflammatory response that affects the joints.

Some of the bacteria that most often cause reactive arthritis are:
chlamydia trachomatis, which can lead to a sexually a transmitted infection (STI)
salmonella, which can cause gastroenteritis
• shigella, which can lead to dysentery
The most common cause is infection from staphylococcus aureus (staph) bacteria that travels to the joint through the blood.
Most common symptomsInflammation in the joints, bladder, urethra, and eyes. Symptoms may present over days or weeks. Severe pain and swelling, typically in the knee joint. Symptoms are acute and present over hours or days.
Risk factorsMore common in:
• adults in their 20s–30s
• males
• people who have inherited the human
leukocyte antigen (HLA) B27 gene
More common in:
• infants under 4 weeks old
• children ages 2–3 years
• males
• children who are immunocompromised,
have hemarthrosis, or hemophilia
• people over 80 years
• adults who have diabetes, skin infections,
rheumatoid arthritis, joint surgery, joint
prosthesis, osteoarthritis, HIV, and other
causes of sepsis
TreatmentIt is not a medical emergency. Treatment may involve:
• pain-relieving medication, such as
disease-modifying anti-rheumatic drugs (DMARDs)
It is a medical emergency. Treatment may involve:
• antibiotics
• joint drainage
• surgical irrigation through arthroscopic surgery to clean out the joint

Some signs and symptoms of reactive arthritis and septic arthritis are similar, while others are distinctly different.

Reactive arthritis

Signs and symptoms of reactive arthritis include:

Septic arthritis

Signs and symptoms of septic arthritis include:

A person should consult a doctor if they experience symptoms of either reactive or septic arthritis.

Both conditions are associated with infection, which could lead to severe complications if a person does not receive treatment.

If someone has recently experienced an infection followed by symptoms of either type of arthritis, they should contact a doctor.

Septic arthritis, in particular, may cause severe complications if a person does not receive treatment. A person should urgently seek medical attention if they have:

  • sudden, severe joint pain
  • swelling around a joint
  • fever and chills
  • a change in skin color around the joint

Medical professionals must examine the joint fluid for diagnosis and treat it promptly with possible surgical drainage and antibiotics.

A doctor may use similar methods to diagnose reactive arthritis and septic arthritis.

There is no specific laboratory test that can confirm whether a person has reactive arthritis or septic arthritis. A doctor may perform several tests to diagnose the conditions. These may include:

  • Physical exam: A doctor may ask questions about a person’s symptoms and medical history and examine the joints, eyes, and genital areas for signs of inflammation.
  • Blood and urine tests: A doctor may order samples of urine and blood for testing in the laboratory to help rule out other conditions. These tests can analyze antibodies, inflammation levels, and signs of infection.
  • X-ray: This may reveal signs of joint damage or swelling, calcium deposits, and other signs that may suggest reactive arthritis. Alongside an X-ray, a doctor may order further imaging tests, such as an MRI.
  • Joint fluid tests: A doctor may take a joint fluid sample to rule out other conditions, such as gout, and to determine what organisms may be the cause of infection in cases of septic arthritis.
  • Tissue samples: Taking samples from the throat, cervix, or urethra may reveal signs of infection in cases of reactive arthritis.
  • Other laboratory tests: Doctors may also perform specific tests to identify the causes of infection in cases of reactive arthritis. This may include stool sample testing to check for salmonella, shigella, or other gastrointestinal bacteria and a genital swab to test for chlamydia.

Reactive arthritis and septic arthritis both have links to infection but have several key differences.

In reactive arthritis, infection in the body, which may be due to bacteria in the gastrointestinal or urinary tracts, triggers an inflammatory immune response. The infection does not affect the joint directly, but the inflammatory reaction may cause pain and inflammation in the joint.

In septic arthritis, bacteria may cause infection in the actual joint, which can result in symptoms such as severe pain and inflammation. It may lead to severe complications if a person does not receive prompt treatment.

If a person experiences symptoms of either condition, they should contact a doctor.