Bacterial arthritis is predominantly caused by Staphylococcus aureus, streptococci, and Neisseria gonorrhoeae. Joint pain and swelling (involving either one or more joints), as well as fever, are three cardinal symptoms seen in these patients. The diagnosis can be made after a proper physical examination, while the determination of the underlying pathogen is achieved through microbiological studies, primarily in the form of blood and synovial fluid cultures.
Bacterial arthritis or infection of the joints and the articular tissues is encountered across all age groups. Overall, Staphylococcus aureus is the most common cause (although Neisseria gonorrhoeae is the number one cause of septic arthritis in younger adults), but streptococcal species (including S. pneumoniae, S. viridans, S. pyogenes), tuberculosis, and a range of both gram-positive and gram-negative bacteria can be responsible for the infection . Several conditions have been described in the literature as potential risk factors for bacterial arthritis, including diabetes mellitus, previous skin infection, rheumatoid arthritis (RA), human immunodeficiency virus (HIV) type 1 infection, as well as increasing age, joint surgery, intravenous drug abuse, and the presence of hip or knee prostheses  . The clinical presentation is centered around three main complaints - joint pain, swelling, and fever (about 40% of patients have a fever of >39C)  . Either one (monoarticular) or more than one (polyarticular) joint can be affected. Gonococcal arthritis is typically polyarticular . The pain is often severe and is exacerbated with minimal movement, thus a decreased range of motion is also an important finding  . Additional less common features of bacterial arthritis include erythema of the skin over the infected joint, rigors, excessive sweating, and constitutional symptoms    .
The physician's ability to recognize signs and symptoms of bacterial arthritis through a detailed patient history and a thorough physical examination is essential for making the diagnosis. Information regarding the onset and course of symptoms should be noted, whereas the assessment of preexisting comorbidities that could predispose individuals to this infection is mandatory. Joint pain and swelling, as principal complaints, need to be evaluated during a physical exam, and as soon as valid clinical suspicion is raised, a complete laboratory workup must be conducted. Serum inflammatory markers, such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), are often elevated in bacterial arthritis . One of the key steps in solidifying the diagnosis is the analysis of synovial fluid . Many studies have confirmed that the white blood cell count of > 50 × 109/L (with a predominance of polymorphonuclear cells, or PMNs) in synovial fluid is highly indicative of septic arthritis   . Furthermore, cultivation of synovial fluid is a definite method for identifying the causative agent of joint infection, and both anaerobic, but more importantly aerobic cultures should be drawn . Gram staining is also described as an important microbiological method in the case of arthritis, but its variable sensitivity is an important limitation  .