1151 The Accuracy and Diagnostic Value of Gram Staining from Joint Aspirates in Suspected Joint Infection

Aim

Septic arthritis is a debilitating pathology. Joint aspirate gram stain is often performed followed by definitive culture. We review the accuracy of gram staining for suspected septic arthritis, and investigate factors associated with aspirate cultures positive for bacterial growth.

Method

We reviewed all theatre performed joint aspirates at a Major Trauma Centre from 2015-2021 for suspected septic arthritis. Information collected included aspirate-site, gram stain and culture results delay, patient demographics, orthopaedic/rheumatological history of affected joint, and various comorbidities.

Outcomes included sensitivity and specificity of the gram stain. Factors that predisposed patients to positive cultures and false-negative gram stains results were calculated via multivariate binary logistic regression.

Results

A total of 408 joint aspirates were included, of which 37 did not receive initial gram staining. Gram staining and culture results’ delay were on average 1.1 and 5.4 days respectively. Logistic regression revealed that prosthetic joint (p = 0.007), past joint infections (p = 0.006), arthritis (p<0.001), hypertension (p = 0.007), currently smoking (p = 0.019) were positively associated with positive cultures, and past joint infections (p = 0.004) were significantly positively associated with false negative gram stain results. Patients on antibiotics at time of aspirate were at higher risk of false-negative gram stain results (OR = 5.538, 95% CI [2.802-10.948], p<0.001).

Conclusions

Whilst the initial gram stain is fast, it has poor sensitivity. We recommend caution when lending any weight to a negative result. Moreover, if the comorbidities highlighted are present or the patient is on antibiotics at time of aspirate, hyper-vigilance should be exercised to risk stratifying patients with any clinical hallmarks of joint infection.