An Evaluation of a Simplified Impression Membrane Sampling Method for the Diagnosis of Microbial Keratitis

Abstract

The purpose of this study was to compare bacterial isolation rate using a corneal impression membrane (CIM) and a sharp instrument for obtaining corneal samples from patients with suspected microbial keratitis (MK). Data was retrospectively collected for all patients that had corneal samples taken for presumed MK between May 2014 and May 2020. Prior to May 2017 samples were collected by scraping the edges of the ulcer with a blade. From May 2017, samples were collected by placing a CIM (Millicell cell culture insert) against the ulcer. All corneal samples were processed using the same conventional diagnostic culture method. A total of 3099 corneal samples were included, of which 1214 (39.2%) were corneal scrapes and 1885 (60.9%) CIMs. Microorganisms were isolated from 235 (19.4%) and 1229 (65.2%) cases using a corneal scrape and CIM, respectively (p < 0.001). Of routinely described pathogenic microorganisms, there were significant increases in the isolations of S. aureus (2.4% to 11.3%) and Serratia (0.5% to 1.7%) using the CIM and no significant changes in the isolations of S. pneumoniae and P. aeruginosa. No significant differences were seen between the isolation rates of fungi or Acanthamoeba species. There was a significant increase in the isolation rates of other Streptococcal species (0.7% to 6.9%) and CNS species, specifically, S. epidermidis (2.1% to 26.2%), S. capitis (0.4% to 2.6%) and S. warneri (0.3% to 1.6%) using the CIM. The simplified CIM sampling method is an effective method for collecting corneal samples from patients with presumed MK in clinical practice.

Rapid Point-of-Care Identification of Aspergillus Species in Microbial Keratitis

“…In this study of the 419 patients recruited, only 62% (259) were culture positive. Often the poor sensitivity is attributed to low microbial yield within the collected scrape samples . Compared with the culture-positive samples, the scrape analysis results demonstrated high sensitivity and NPV (0.89 and 0.97) and low negative LR (0.12), indicating that there were few false-negative results and that the samples tested on the LFDs contained antigen (an extracellular glycoprotein) above the limit of detection.…”

“…Often the poor sensitivity is attributed to low microbial yield within the collected scrape samples. 38,39 Compared with the culturepositive samples, the scrape analysis results demonstrated high sensitivity and NPV (0.89 and 0.97) and low negative LR (0.12), indicating that there were few false-negative results and that the samples tested on the LFDs contained antigen (an extracellular glycoprotein 31 ) above the limit of detection. While not included within the formal AspLFD analysis, 5 of the 76 culturenegative, fungal smear-positive scrape samples also had positive AspLFD results, suggesting that these patients likely had a missed Aspergillus species infection.…”

Big data in corneal diseases and cataract: Current applications and future directions

“…In view of its significant impact on human health, healthcare systems and economy, it is therefore not surprising to observe a vast amount of literature on IK, encompassing the epidemiology, risk factors, clinical characteristics, causative organisms, management, and outcomes of the disease. Large IK studies published in the recent years are summarized in Table 2 (Lin et al, 2017 , 2019 ; Tan et al, 2017 ; Khor et al, 2018 ; Peng et al, 2018 ; Green et al, 2019 ; Tavassoli et al, 2019 ; Asbell et al, 2020 ; Khoo et al, 2020 ; Kowalski et al, 2020 ; Somerville et al, 2021 ; Ting et al, 2021d ).…”

“…. (Lin et al, 2017(Lin et al, , 2019Tan et al, 2017;Khor et al, 2018;Peng et al, 2018;Green et al, 2019;Tavassoli et al, 2019;Asbell et al, 2020;Khoo et al, 2020;Kowalski et al, 2020;Somerville et al, 2021;Ting et al, 2021d).…”

Therapy for contact lens-related ulcers

“…Culturing contact lenses, cases, and solutions can be useful although studies have shown a wide range of concordance of results between corneal and contact lens case samples [23 ▪▪ ,25]. A sterile impression membrane may provide diagnostic yield similar to corneal scraping [26]. Lesions where only deeper stroma is involved may benefit from passage and culture of a suture, or corneal biopsy for histopathology and culture of the deeper layers under the biopsy [23 ▪▪ ,27].…”