Risk factors are listed in Table 54-1. Comorbidity may increase not only the risk of infectious arthritis but also disease severity. Risk of joint infection is substantially increased in patients with RA or in others with a past history of joint infection or with a prosthetic joint implant. Sources of infection include otitis media, umbilical catheters, central lines, femoral venipunctures, meningitis, and adjacent osteomyelitis. Neisseria gonorrhoeae is the most common bacterial cause in adults.
Infections commonly begin in the urinary tract or skin.
The predominant anaerobic organisms are Propionibacterium acnes, Peptostreptococcus magnus, Fusobacterium sp, Clostridium sp, and Bacteroides sp. P. acnes causes infections in joints with prostheses, trauma, or prior surgery. Factors predisposing to anaerobic infection include penetrating trauma, arthrocentesis, recent surgery, joint prosthesis, contiguous infection, diabetes, and malignancy. Animal bites may give rise to joint infections typically caused by S. aureus or organisms of the oral flora common to the animal. Pasteurella multocida causes half the infections resulting from dog or cat bites.