Viruses such as rubella, parvovirus B19, chikungunya, and HIV infection can also cause septic arthritis. Prosthetic joint infection – Artificial joint infection are usually caused by coagulase negative Staphylococci, Staphylococcus aureus, and gram negative bacilli. Concurrent infections by multiple organisms is also reported in 20% of the cases. The risk factors of prosthetic joint infections are:  previous fracture, seropositive rheumatoid arthritis, obesity, revision arthroplasty, and surgical site infections. List of organisms
Staphylococci (40%)Staphylococcus aureus – the most common cause in most age groups. Can be caused by skin infection, previously damaged joint, prosthetic joint or intravenous drug use. coagulase-negative staphylococci – usually due to prosthetic joint
Streptococci – the second-most common cause (28%)Streptococcus pyogenes – a common cause in children under 5
Streptococcus pneumoniae
Group B streptococci – a common cause in infants
Haemophilus influenzae
Neisseria gonorrhoeae – the most common cause of septic arthritis in young, sexually active adults. Multiple macules or vesicles seen over the trunk are a pathognomonic feature. Neisseria meningitidis
Escherichia coli – in the elderly, IV drug users and the seriously ill
Pseudomonas aeruginosa – IV drug users or penetrating trauma through the shoe
M. tuberculosis, Salmonella spp. and Brucella spp. – cause septic spinal arthritis
Eikenella corrodens – human bites
Pasteurella multocida, bartonella henselae, capnocytophaga – animal bites or scratches
Fungal species – immunocompromised state
Borrelia burgdorferi – ticks, causes lyme disease
Spirillum minus, Streptobacillus moniliformis– rat bites

Diagnosis
Septic arthritis should be considered whenever a person has rapid onset pain in a swollen joint, regardless of fever.
General guidelines are as follows:

Gram positive cocci – vancomycin
Gram negative cocci – Ceftriaxone
Gram negative bacilli – Ceftriaxone, cefotaxime, or ceftazidime
Gram stain negative and immunocompetent – vancomycin
Gram stain negative and immunocompromised – vancomycin + third generation cephalosphorin
IV drug use (possible pseudomonas aeruginosa) – ceftazidime +/- an aminoglycosideOnce cultures are available, antibiotics can be changed to target the specific organism. After a good response to intravenous antibiotics, people can be switched to oral antibiotics. The duration of oral antibiotics varies, but is generally for 1–4 weeks depending on the offending organism. Repeated daily joint aspiration is useful in the treatment of septic arthritis. Every aspirate should be sent for culture, gram stain, white cell count to monitor the progress of the disease. Both open surgery and arthroscopy are helpful in the drainage of the infected joint. During surgery, lysis of the adhesions, drainage of pus, and debridement of the necrotic tissues are done. Close follow up with physical exam & labs must be done to make sure the person is no longer feverish, pain has resolved, has improved range of motion, and lab values are normalized.In infection of a prosthetic joint, a biofilm is often created on the surface of the prosthesis which is resistant to antibiotics. Surgical debridement  is usually indicated in these cases. A replacement prosthesis is usually not inserted at the time of removal to allow antibiotics to clear infection of the region. People that cannot have surgery may try long-term antibiotic therapy in order to suppress the infection.