context: Septic arthritis is also known as infectious arthritis, and is usually caused by bacteria. It can also be caused by a virus or fungus. The condition is an inflammation of a joint that's caused by infection. Typically, septic arthritis affects one large joint in the body, such as the knee or hip. Less frequently, septic arthritis can affect multiple joints. Septic arthritis usually is caused by bacteria that spread through the blood stream from another area of the body. It can also be caused by a bacterial infection from an open wound or an opening from a surgical procedure, such as knee surgery. In adults and children, common bacteria that cause acute septic arthritis include staphylococcus and streptococcus. These foreign invaders enter the bloodstream and infect the joint, causing inflammation and pain. Other infections, such as those caused by viruses and fungi, can also cause arthritis. Viruses include: Hepatitis A, B, and C Parvovirus B19 Herpes viruses HIV ( AIDS virus) HTLV-1 Adenovirus Coxsackie viruses Mumps Fungi that can cause arthritis include histoplasma, coccidiomyces, and blastomyces. These infections are usually lslower to develop than bacterial infections. Young children and elderly adults are most likely to develop septic arthritis. People with open wounds are also at a higher risk for septic arthritis. In addition, people with a weakened immune system and those with pre-existing conditions such as cancer, diabetes, intravenous drug abuse, and immune deficiency disorders have a higher risk of septic arthritis. In addition, previously damaged joints have an increased likelihood of becoming infected. Symptoms of septic arthritis usually come on rapidly with intense pain, joint swelling, and fever. Septic arthritis symptoms may include: Chills Fatigue and generalized weakness Fever Inability to move the limb with the infected joint Severe pain in the affected joint, especially with movement Swelling (increased fluid within the joint) Warmth (the joint is red and warm to touch because of increased blood flow) A procedure called arthrocentesis is commonly used to make an accurate diagnosis of septic arthritis. This procedure involves a surgical puncture of the joint to draw a sample of the joint fluid, known as synovial fluid. Normally, this fluid is sterile and acts as a lubricant. During arthrocentesis, a needle is inserted into the affected joint to collect fluid from the joint. The fluid sample is sent to a lab for evaluation. The lab will perform a white cell count on the fluid, which will usually very high. The lab will also try to culture bacteria or other organisms. This will help the doctor determine if an infection is present and which organism is causing it. X-rays are typically done to look for joint damage. Blood tests can also be used to monitor inflammation. MRI scanning is sensitive in evaluating joint destruction but is less useful in the early stages . Blood tests can also be taken to detect and monitor inflammation. Septic arthritis treatments include using a combination of powerful antibiotics as well as draining the infected synovial fluid from the joint. It's likely that antibiotics will be administered immediately to avoid the spread of the infection. Intravenous ( IV) antibiotics are given, usually requiring admission to the hospital for initial treatment. The treatment, however, may be continued on an outpatient basis at home with the assistance of a home health nursing service. Initially, empiric antibiotics are chosen to cover a wide range of infections. If the bacteria can be identified, antibiotics specific to that organism are used. It may take four to six weeks of treatment with antibiotics to ensure complete eradication of the infectious agents. Drainage of the infected area is critical for rapid clearing of the infection. Drainage is performed by removing the fluid with a needle and syringe. Often the draining occurs daily or with multiple surgical procedures. The exact method depends on the location of the joint. Using arthroscopy, your doctor can irrigate the joint and remove the infected tissue. If drainage cannot be accomplished with joint aspirations or arthroscopy, open joint surgery is often necessary to drain the joint. If the fluid buildup is significant, the drains are left in place to remove excess fluid that may build up after the surgery.