Lateral-Flow Device Accurately Identifies Aspergillus-Caused Microbial Keratitis

Venkatesh Prajna, MD

Credit: Aravind Eye Hospital

A rapid lateral-flow device (LFD) using corneal scrape and swab samples achieves high diagnostic accuracy in the detection of Aspergillus causing microbial keratitis, without the need for a dedicated laboratory, according to new results from a diagnostic feasibility study.¹

Microbial keratitis remains a common cause of unilateral visual impairment, blindness, and eye loss for patients in low- and middle-income countries. Microbial culture is considered the gold standard for diagnosis but requires invasive corneal scraping for retrieval of microbiological material and yields positive results only half of the time.²

“This diagnostic feasibility study suggests that the LFD technology could offer an alternative gold standard approach for the diagnosis of microbial keratitis… particularly if multiplexed LFDs are developed to simultaneously screen several important microbial keratitis pathogens," wrote the investigative team, led by Bethany Mills, PhD, of the Queen’s Medical Research Institute, University of Edinburgh, and Venkatesh Prajna, MD, of the Cornea & Refractive Surgery Services, Aravind Eye Hospital.¹

For this analysis, the investigative team evaluated the diagnostic performance of an Aspergillus-specific LFD to identify Aspergillus species in corneal scrape and swab samples in eyes presenting with microbial keratitis. The study was conducted between May 2022 and January 2023 at a tertiary eye hospital in India and all participants were recruited at their first presentation to the clinic.

During standard-of-care diagnostic sampling, investigators collected a minimally invasive corneal swab and scrape and analyzed by the LFD. The main outcome was the sensitivity and specificity of the Aspergillus-LFD with corneal samples collected from these patients with microbial keratitis. A photograph of the LFD was assessed using a ratiometric approach developed for analysis.

A total of 198 scrape samples and 40 swab samples were included in the Aspergillus-LFD performance analysis. Participants who met the inclusion criteria had a mean age of 51 years and 126 individuals (63.6%) were male. Per the culture report, the prevalence of Aspergillus species detected by the LFD was 17.7% (35 of 198) in the corneal scrape samples and 42.5% (17 of 40) in the swab samples.

Results from the ratiometric analysis of the scrape samples revealed the Aspergillus-LFD achieved high sensitivity (0.89; 95% CI, 0.74 - 0.95), high negative predictive value (0.97; 95% CI, 0.94 - 0.99), and a low negative likelihood ratio (0.12; 95% CI, 0.05 - 0.30). Overall, the results were equivalent between visual inspection and ratiometric analysis. Meanwhile, the device sensitivity (0.95; 95% CI, 0.91 - 0.98), positive predictive value, positive likelihood ratio (18.05; 95% CI, 9.09 - 35.84), and accuracy (0.94; 95% CI, 0.90 - 0.97) were all significantly improved with ratiometric analysis.

The 40 samples included in the Aspergillus-LFD analysis had distinctly poor specificity (0.04; 95% CI, 0.00 - 0.21) due to the high number of false-positive LFD results. The swab-based radiometric analysis showed the Aspergillus-LFD was equivalent to visual inspection, with high sensitivity (0.94; 95% CI, 0.73 - 1.00), high negative predictive value (0.95; 95% CI, 0.76 - 1.00), and low negative likelihood ratio (0.07; 95% CI, 0.01 - 0.48), as well as greatly improved accuracy (0.88; 95% CI, 0.73 - 0.96).

These findings suggest that sufficient antigen was collected from the ocular surface using the minimally invasive collection method, meaning swabs could be utilized in settings with limitations to collection, including the community and primary care settings.

“This finding is of particular importance because swabs could be used to collect corneal samples from patients with suspected microbial keratitis in settings where the routine method of specimen collection by scraping is not possible, such as primary care,” investigators wrote.

References

1. Gunasekaran R, Chandrasekaran A, Rajarathinam K, et al. Rapid Point-of-Care Identification of Aspergillus Species in Microbial Keratitis. JAMA Ophthalmol. Published online September 28, 2023. doi:10.1001/jamaophthalmol.2023.4214
2. Ung L, Bispo PJM, Shanbhag SS, Gilmore MS, Chodosh J. The persistent dilemma of microbial keratitis: global burden, diagnosis, and antimicrobial resistance. Surv Ophthalmol. 2019;64(3):255-271. doi:10.1016/j.survophthal.2018.12.003