Infectious Arthritis Definition and Symptoms

Also referred to as septic arthritis, Bacterial arthritis, or Non-gonococcal bacterial arthritis, Infectious Arthritis is an infection in the fluid in tissues of the joints that is usually caused by bacteria, but sometimes is triggered by viruses or fungi.(1)

Infectious arthritis can happen to people of any age, sex or gender. Infants can also be affected by infectious arthritis when an infection settles in one of their joints.

Generally, younger children do not move the infected joints because moving or touching it is painful. Younger children may refuse to walk and older children and adults will find that the symptoms began over several hours or a few days.(2)

Symptoms of Septic Arthritis

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The infected joint becomes red and warm and moving it or touching it is very painful. Fluid (synovial) will collect in the joint and cause it to swell and stiffen.

Individuals can also suffer from fever and chills. People who suffer from a more chronic infectious arthritis that’s caused by mycobacteria will have less dramatic symptoms.

The joints that are most commonly infected are the knee, shoulder, wrist, hip, elbow and fingers. Most of the time infectious arthritis will affect only one joint.

Infectious arthritis in younger, sexually active individuals could be caused by Neisseria gonorrhea bacteria. 3 Gonococcal infectious arthritis present symptoms in one of two possible ways:

Asymmetric polyarthritis, often associated with tenosynovitis and petechial skin rash
• Isolated purulent monoarthritis, which in some cases may occur after the asymmetric polyarthritis

Symptoms in newborns or infants include:

• Cries when infected joint is moved
• Irritability
• Fever
• Inability to move limbs with infected joints


The most frequent cause of infectious arthritis is bacteria. These include Staphylococcus aureus and Haemophilus influenzae. Other bacteria causing infectious arthritis include the spirochete bacterium which causes Lyme disease, E. coli, Pseudomonas spp. and Mycobacterium tuberculosis.

People who are at risk are those who have abnormal joints because of arthritic damage or who develop an infection that reaches their bloodstream. For example, an older individual, who has an infection in their bloodstream can fall and injure their knee.

Bleeding from the knee results in an infectious arthritis because the blood enters the joint space. A joint can also be infected directly if it is contaminated during surgery or from an injury.

The most likely bacteria to cause an infected joint will depend upon the individual’s age.

For instance, researchers know that infected infants and children will experience staphylococci infections while gonococci and streptococci most often infect older children and adults. Viruses, such as HIV, parvovirus and hepatitis B, can infect the joints the people of any age.


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If your physician suspects that you may have an infectious arthritic joint they will require a sample of the fluid which is removed with a sterile needle as soon as possible.

This fluid will be examined for white blood cells as well as cultured for bacteria and other organisms. In this way the doctor can recommend a treatment protocol which is specifically aimed at the organisms which are causing your infection.

Doctors will usually order blood tests as well to determine whether or not the individual also has it in their bloodstream. Sputum culture, spinal fluid culture and urine culture may also be collected looking for bacteria in order to determine the source of the infection.

The physician may or may not want x-rays of the involved joint because they are not diagnostic of an acute infection. However they can also pick up other conditions that are under consideration, such as fractures.

Any abnormalities in the early stages of infectious arthritis are limited to the soft tissue will not show under x-ray. However, after 10 to 14 days of being untreated the destruction will be visible on x-ray.

Without immediate treatment, the joint can be destroyed within days, sometimes within hours. Prompt treatment must be started to prevent this from happening, even before the laboratory has identified the infecting organisms.


The physician will recommend antibiotics that are broad spectrum, kill the most likely bacteria within a broad range until the infecting organism has been identified. 10 days of antimicrobials is typically enough in pediatric cases.4

These antibiotics will be given first by a vein to ensure that enough of the drug reaches the joint. If the right antibiotic was chosen there will be improvement within the first 48 hours.

The physician may choose to do a needle aspiration of the joints in order to remove as much pus as possible to prevent damage. If a needle aspiration is difficult or unsuccessful, the doctor may recommend an arthroscopic procedure to drain the fluid.

The actual infection of the fluid is in the synovial or peri-articular tissues. About 50% of the children who have a joint infection are less than three years old but with routine childhood vaccination for Haemophilus influenza and Streptococcus pneumonia this incidence is decreasing.

Individuals who are at risk for infectious arthritis are those who are taking immune suppression medicines, intravenous drug abusers, have had a past history of joint disease injury or surgery, or who may have an underlying medical conditions such as diabetes, alcoholism, sickle cell or rheumatic disease.


(1) PubMed Health: Septic Arthritis

(2) MedlinePlus: Septic Arthritis

(3) Malik S, Chiampas G, Leonard H (November 2010). “Emergent evaluation of injuries to the shoulder, clavicle, and humerus“. Emerg Med Clin North Am 28 (4): 739–63.

(4) Peltola H, Pääkkönen M, Kallio MJ, Kallio PE. (May 2009). “Prospective, randomized trial of 10 days versus 30 days of antimicrobial treatment, including a short-term course of parenteral therapy, for childhood septic arthritis.”. Clin. Infect. Dis. 48 (9): 1201–10. doi:10.1086/597582. PMID 19323633.

(5) MayoClinic: Septic Arthritis

Top Photo by Pacific Northwest National Laboratory