The classical presentation of infectious arthritis is acute onset of pain, warmth and swelling of a single joint.
The range of motion is usually decreased.
The knee is the most commonly affected but any joint may be involved.
Fever and chills may be present.
More than 1 joint may be involved in patients with pre-existing joint disease, other inflammatory conditions or severe sepsis, and in some patients infected with certain pathogens eg N gonorrheae, N meningitidis and Salmonella spp.
Infectious arthritis must always be a part of the differential diagnosis in a patient with an acute monoarthritis. 

Infectious%20arthritis Diagnosis


  • Monitor patient for improvement of clinical signs and symptoms
  • Levels of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) may be used to evaluate response to treatment
  • Specialist referral should be considered in patients with features of sepsis for possible drainage and parenteral antibiotic therapy
  • Continue empiric treatment if patient is improving and cultures are negative
  • Serial analysis of the synovial fluid should show a decreasing white blood cell (WBC) count and should revert to the sterile state with treatment
  • If a patient does not improve with appropriate treatment, consider:
    • Revision of antibiotic therapy
    • Open drainage of joint, biopsy and repeat culture, washout or debridement may be required
    • Repeating tests to uncover a possible non-infectious cause of arthritis
    • Consider specialist referral
  • Outpatient parenteral antibiotic therapy may be considered in patients in whom it is not feasible to complete treatment with oral antibiotics
    • A functioning outpatient parenteral antimicrobial therapy (OPAT) program should have a complete and qualified health care team, efficient means of communication, guidelines for follow-up, testing and other interventions, written policies and procedures and outcomes monitoring
    • A candidate for inclusion in an OPAT program should be willing to participate in the program and should have a home environment that is sufficient to support care


  • Family history of gout
  • Sexual history including history of N gonorrhoeae infection
  • Travel and occupational history
  • Diet and alcohol consumption

Physical Examination

  • Patients most often present with a red, warm, swollen and very tender joint
    • Affected joint may also present with effusion and severe restriction of movement
  • Exam should focus on the involved and contralateral joint and surrounding area including the skin and soft tissue
    • A general exam should be performed to search for other joint involvement, look for systemic manifestations of disease and seek extra-articular sources of infection
    • Gonococcal infections may manifest with fever, multiple painless macules and papules on the arms, legs or trunk, and tenosynovitis
    • Patients with rheumatoid arthritis may present exacerbation of inflammation in one or more joints
  • In children with infectious arthritis of the hip, the hip may be kept flexed and externally rotated, with severe pain on motion
  • Few physical signs may be found in patients with infectious arthritis of the spine, sacroiliac joints and hips
  • The absence of fever does not rule out infectious arthritis

Laboratory Tests

Synovial Fluid Exam 

  • Synovial fluid aspiration is the most important test for diagnosing infectious arthritis and should be done for all patients suspected of having infectious arthritis
    • Synovial fluid culture is positive in 50-60% of cases
    • Synovial fluid glucose is usually decreased while protein and lactate dehydrogenase are usually increased in both inflammatory and infectious causes of arthritis
  • Gram stain, culture, white blood cell (WBC) count with differential should be done
    • Cornerstone of rapid and reliable confirmation of diagnosis 
    • Gram stain is positive in only 60-80% of cases; a negative Gram stain and/or culture does not exclude the diagnosis of infectious arthritis
    • A WBC count of >50,000 cells/mm3 with neutrophil predominance is highly suggestive of bacterial arthritis
  • Routine polymerase chain reaction (PCR) is not recommended; may be useful in prosthetic joint infection to differentiate between septic and aseptic loosening and in culture-negative patients with similar presentation as reactive arthritis
  • Polarizing microscopy to evaluate crystals should be performed
  • Synovial biopsy is the most sensitive (95%) way to confirm a diagnosis of mycobacterial infectious arthritis

Blood Culture

  • Should be obtained in all patients suspected of having infectious arthritis
  • Positive in 50% of cases

Complete Blood Count (CBC), Erythrocyte Sedimentation Rate (ESR), C-reactive Protein (CRP)

  • Used to determine presence of infection or inflammation; ESR and CRP are useful for monitoring treatment response
  • Leukocytosis is usually present (leukocyte count of 50,000-150,000 cells/mm3)
  • ESR is usually >20 mm/hour
  • CRP is usually raised; a normal CRP is a good negative predictor for infectious arthritis
  • Normal levels of ESR, CRP and/or WBC do not rule out infectious arthritis

Other Laboratory Tests

  • Blood urea nitrogen (BUN), creatinine and liver function tests should be taken to detect end-organ damage, a poor prognostic factor in infectious arthritis
  • Appropriate specimens from other sites (eg cervix, urethra and throat) should be taken in patients in whom genitourinary, respiratory or other infections are being considered


  • Plain x-rays of affected joints are not very helpful in diagnosing infectious arthritis but may act as a baseline to help exclude osteomyelitis or other abnormalities of the bone
    • X-rays done during early infection are usually normal but may show soft tissue swelling, displacement of the fat pad, or joint space widening secondary to localized edema
  • Magnetic resonance imaging (MRI) is a sensitive test for distinguishing infectious arthritis from osteomyelitis and demonstrates adjacent soft tissue edema and abscesses
  • Computed tomography (CT) scan is helpful in detecting effusions and inflammation in joints that are difficult to examine because of complex anatomy (eg hip and shoulder)
  • Ultrasonography may detect fluid in suspected infectious arthritis of the hip and may be used to perform an imaging-guided joint aspiration
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