Association Between Season, Temperature and Causative Organism in Microbial Keratitis in the UK.

PURPOSE: Microbial keratitis (MK) is a major cause of corneal blindness worldwide. Variations in season and temperature can affect MK incidence due to specific causative organisms; however, few studies have examined these factors in the UK. METHODS: Retrospective review of all corneal scrapes from patients with MK presenting to Manchester Royal Eye Hospital, UK, between January 2004 and December 2015. Manchester's monthly temperature data were obtained from Met Office UK. Analysis was performed using logistic regression. RESULTS: From 4229 corneal scrapes, 1539 organisms grew (90.6% bacteria, 7.1% fungi, and 2.3% Acanthamoebae sp.). Gram-positive bacteria grew with increasing temperature [odds ratio (OR) 1.62, 95% CI: 1.11-2.39, P = 0.014], and fungi grew with decreasing temperature (OR 0.29, 95% CI: 0.16-0.51, P < 0.001). Moraxella sp. grew with decreasing temperature (OR 0.91, 95% CI: 0.86-0.96, P = 0.001). Compared with winter, overall culture positivity was significantly less likely in summer (OR 0.57, 95% CI: 0.38-0.87, P = 0.008) and spring (OR 0.65, 95% CI: 0.43-0.99, P = 0.045). Gram-negative bacteria were more likely in summer (OR 1.48, 95% CI: 1.06-2.09, P = 0.022) and autumn (OR 1.75, 95% CI: 1.24-2.47, P = 0.001). Candida sp. were less likely in summer (OR 0.25, 95% CI: 0.07-0.82, P = 0.027) and autumn (OR 0.18, 95% CI: 0.05-0.62, P = 0.009), and Acanthamoeba sp. were less likely in summer (OR 0.39, 95% CI: 0.15-0.92, P = 0.037) and spring (OR 0.26, 95% CI: 0.08-0.69, P = 0.011). CONCLUSIONS: Herein we report variation in the incidence of MK-causing organisms by season and temperature; this finding may aid clinicians in predicting possible causative organisms for MK at differing times of the year.

False-negative rate of gram-stain microscopy for diagnosis of septic arthritis: suggestions for improvement.

We quantify the false-negative diagnostic rate of septic arthritis using Gram-stain microscopy of synovial fluid and compare this to values reported in the peer-reviewed literature. We propose a method of improving the diagnostic value of Gram-stain microscopy using Lithium Heparin containers that prevent synovial fluid coagulation. Retrospective study of the Manchester Royal Infirmary microbiology database of patients undergoing synovial fluid Gram-stain and culture between December 2003 and March 2012 was undertaken. The initial cohort of 1896 synovial fluid analyses for suspected septic arthritis was reduced to 143 after exclusion criteria were applied. Analysis of our Gram-stain microscopy yielded 111 false-negative results from a cohort size of 143 positive synovial fluid cultures, giving a false-negative rate of 78%. We report a false-negative rate of Gram-stain microscopy for septic arthritis of 78%. Clinicians should therefore avoid the investigation until a statistically significant data set confirms its efficacy. The investigation's value could be improved by using Lithium Heparin containers to collect homogenous synovial fluid samples. Ongoing research aims to establish how much this could reduce the false-negative rate.

Bacterial susceptibility to topical antimicrobials and clinical outcome in bacterial keratitis.

PURPOSE: To investigate the relationship between the susceptibility of bacteria to topical antimicrobials and clinical outcome in microbial keratitis. METHODS: Clinical outcome data were collected from patients with microbial keratitis from whom a bacterium had been isolated during the period 2003 to 2006. The minimum inhibitory concentration (MIC) was determined for the isolates against 10 antimicrobials. The determinants of the primary clinical outcome, the ratio of healing time (closure of epithelial defect) to ulcer size (HT/UA), was analyzed in a general linear model. RESULTS: Complete clinical outcome and MIC data were available for 421 patients. Sixteen (4%) patients required enucleation and 23 (5%) surgical treatment; in 382 (91%) the ulcer healed with intensive topical antimicrobial therapy. There were significant correlations between HT/UA and organism type (P = 0.001), nearest distance of the ulcer to the limbus (0.02), and MIC of the first antimicrobial used or lowest MIC of combined therapy (P = 0.006). In a model including patients who received monotherapy with a fluoroquinolone who had no subsequent change in their treatment and whose ulcers healed without surgical intervention, there were significant linear associations between clinical outcome and MIC for Pseudomonas spp. (P = 0.047), Staphylococcus aureus (P = 0.04), and Enterobacteriaceae (P = 0.045), but not for Streptococcus spp. (P = 0.85) and coagulase-negative staphylococci (CNS) (P = 0.88). CONCLUSION: With fluoroquinolone monotherapy, there was significant association between the MIC of the antimicrobial prescribed and the clinical outcome with all bacteria except CNS and Streptococcus spp. The approach used in this study, if used prospectively, could allow topical breakpoint susceptibility concentrations to be determined for individual antimicrobial and bacterial combinations.