Acute bacterial arthritis is a potentially serious and rapidly progressive infection that may involve native or prosthetic joints. The epidemiology, pathophysiology, repertoire of potential infecting pathogens, clinical presentation and treatment differ for these two forms of infectious arthritis, but both are associated with significant morbidity and mortality. Infectious arthritis of native and prosthetic joints may be caused by viruses, or fungi, but the most common cause is bacteria.
Acute Bacterial Arthritis
The burden of septic arthritis in the general population is considerable. The incidence of native joint septic arthritis is approximately 5 cases per 100,000 persons per year and is much higher in patients with rheumatoid arthritis (1,2). Between 1% and 5% of joints with indwelling prostheses become infected and the total number of infections per year is increasing due to a rise in the number of patients who have had prosthetic replacement surgery (3). The mortality from joint infection is difficult to estimate due to differing comorbidity in afflicted patients, but is likely between 15% and 30% (4-6). There is substantial morbidity from these infections because of decreased joint function and mobility, and in cases involving joint prostheses from the excisional or exchange arthroplastic surgery that is often required for treatment.
The most common route of infection for native joint infection is hematogenous (1), but may also be a result of direct inoculation of bacteria through trauma or joint surgery (including arthrocentesis, corticosteroid injection, or arthroscopy) (7), or via contiguous spread from adjacent infected soft tissue or bone (1,8). While hematogenous infection of prosthetic joints occurs, the majority of these infections are the result of joint contamination in the course of implantation surgery or post-surgical wound infection (3). Host factors that increase the risk of septic arthritis include pre-existing joint disease (especially rheumatoid arthritis), immunosuppression, diabetes mellitus, malignancy, chronic renal failure, intravenous drug use, severe skin diseases, and advanced age (1,2,4,6). The extent of joint injury resulting from infection depends on the virulence of the infecting pathogen and degree of host immune response (9).
The most common causes of bacterial septic arthritis are outlined in Table 1. In adults, the most frequent etiology is S. aureus (37–65% of cases) (1,4,6,8,12,15,16) followed by Streptococcus sp. (12,15). An increasing percentage of S. aureus isolated from septic joints are resistant to antistaphylococcal penicillins and cephalosporins (methicillin-resistant S. aureus, MRSA). In adults with diabetes, malignancy, and genitourinary structural abnormalities, group B Streptococcus is a frequently isolated pathogen (5,6,17). Gram-negative bacilli are commonly found in neonates, intravenous drug users, and immunocompromised hosts (18). N. gonorrhoeae is a significant cause of bacterial arthritis in sexually active adults and adolescents (19) and Kingella kingae and Haemophilus influenzae are likely pediatric isolates (20,21). Joint infections that follow bite trauma usually are seen in the small joints of the hand and involve Pasteurella multocida in the case of animal bites, and Eikenella corrodens in the case of humans bites (22-24). Polymicrobial floras are found in up to 8% of cases of septic arthritis.
The bacteria that cause prosthetic joint arthritis vary depending on the stage of infection as defined by the elapsed time after implantation surgery (Table 1 on page 31). The coagulase negative staphylococci are the most common (30–43% of cases) (3,10), followed by S. aureus (12–23%) (25).
Nonbacterial pathogens that may cause septic arthritis include viruses, fungi, and mycobacteria. Viral arthritis is often associated with a systemic febrile illness and other manifestations of infection such as rash. Parvovirus B19 is the most common viral arthritide, presenting as a symmetric polyarticular arthritis involving the joints of the hand as well as larger joints (26). The classic red “slapped cheeks” associated with this viral infection in children is usually not present in adults, although a faint lacy reticular rash may be seen.