Gram stain microscopy in septic arthritis.

Area of Science:

• Orthopedics
• Infectious Diseases
• Microbiology
• Diagnostic Pathology

Background:

• Septic arthritis is a severe joint infection requiring prompt diagnosis and treatment to prevent rapid joint destruction.
• Annual incidence is 10 per 100,000, rising to 70 per 100,000 in at-risk populations (e.g., rheumatoid arthritis, immunocompromised patients).
• Gram stain is a common initial diagnostic test for suspected septic arthritis.

Purpose of the Study:

• To evaluate the clinical utility of Gram stain for diagnosing septic arthritis.
• To determine the sensitivity and specificity of Gram stain in identifying septic arthritis.
• To assess the impact of Gram stain results on clinical decision-making for joint infections.

Main Methods:

• Retrospective case series analysis of joint aspirates from May 2015 to April 2018 at a single center.
• Inclusion of 830 samples from both native (701 cases) and prosthetic (129 cases) joints.
• Comparison of Gram stain results with final culture results for all analyzed samples.

Main Results:

• A discrepancy between Gram stain and culture results was observed in 74 cases (9%).
• The sensitivity of Gram stain for detecting septic arthritis was found to be 22%.
• The specificity of Gram stain was high, recorded at 99.6%.

Conclusions:

• Gram stain demonstrates low sensitivity in diagnosing septic arthritis, indicating a high rate of false negatives.
• Despite low sensitivity, Gram stain exhibits high specificity, meaning positive results are generally reliable.
• Clinicians should maintain a low threshold for considering septic arthritis even with negative Gram stain results, emphasizing clinical presentation and biochemical markers.