Diagnostic value of culture results from aqueous tap versus vitreous tap in cases of bacterial endophthalmitis

ObjectiveTo investigate the concordance between aqueous and vitreous tap culture results among different types of bacterial endophthalmitis.Methods and analysisThis retrospective cohort analysis included all cases diagnosed with endophthalmitis at Moorfields Eye Hospital between January 2008 and March 2020. Aqueous and vitreous samples obtained simultaneously at presentation. Samples were evaluated for sensitivity, specificity, negative and positive predictive values.ResultsA total of 217 patients (217 eyes) were included in the study. Postsurgical endophthalmitis was the most common type of endophthalmitis and diagnosed in 35.9% of the cases. The rate of positive culture results was 32.2% from vitreous tap and 21.7% from aqueous tap. The culture yield through vitreous sampling was 15.7% when aqueous culture results were negative, and in 5.1%, the aqueous sample was positive when the vitreous tap results were negative. Considering the vitreous tap as the gold standard, aqueous sample culture results showed a statistically significant high specificity and positive predictive values in cases of postsurgical endophthalmitis, late-onset endophthalmitis associated with glaucoma procedures, postintravitreal injection and endophthalmitis associated with bacterial keratitis. Coagulase Negative Staphylococcus was the most common organism isolated from vitreous and aqueous samples.ConclusionsEven though the sensitivity and specificity of aqueous tap are low, our results show that in a few cases it identified important organisms, otherwise missed by vitreous sampling alone. Culture of vitreous sample remains the gold standard for isolation of pathogen in bacterial endophthalmitis, but aqueous samples should also be obtained as an adjunct for the diagnosis.