In this study, investigators developed and tested a novel multiplex PCR test (Strip PCR) for 24 common ocular infectious-disease pathogens.
Study design
In this study, investigators developed and tested a novel multiplex PCR test (Strip PCR) for 24 common ocular infectious-disease pathogens. The study included 722 ocular fluid samples collected from patients at 14 hospitals in Japan. Each sample was analyzed with both the strip PCR and with quantitative PCR (qPCR), which is the gold standard test. The strip PCR test is designed to look for 24 pathogens—HSV1, HSV2, VZV, EBV, CMV, HHV6, HHV7, HHV8, HTLV-1, adenovirus, mycobacterium TB, Treponema pallidum, P acnes, bacterial 16S ribosomal RNA, Candida albicans, Candida glabrata, Candida krusei, Aspergillus, Fusarium, fungal 28S rRNA, Toxoplasma, Toxocara, Chlamydia trachomatis and Acanthamoeba—from a 50-uL aqueous or vitreous fluid sample.
Outcomes
Several control patient samples without a clinical diagnosis of uveitis demonstrated a positive test result with both the strip PCR and qPCR , which was suggestive of a contamination. These organisms were presumed to be present on laboratory surfaces or in clinical environments, and were excluded from the study.
The Strip PCR was optimized for 9 pathogens in this analysis: HSV1, HSV2, VZV, HTLV-1, HHV6, EBV, CMV, T gondii and T pallidum. Of 722 samples, 255 tested positive for a pathogen with qPCR. Of those 255 samples, 252 tested positive with Strip PCR, indicating the test had a high sensitivity (98.8%), specificity (98.5%), positive predictive value (98.8%) and negative predictive value (98.5%) compared with qPCR.
The three samples that tested negative with Strip PCR (and positive with qPCR) were for herpetic anterior uveitis, CMV retinitis, and ocular toxoplasmosis. No pathogen DNA was detected with either test in 67 samples with clinical diagnosis of noninfectious uveitis/ocular inflammation, including lymphoma, sarcoidosis, acute anterior uveitis, Posner-Schlossman syndrome, VKH, Behcet disease, and lens-induced uveitis. The most frequently detected pathogen was CMV (115 samples).
Limitations
The study excludes a significant number of the organisms for possible contamination. This study was conducted in a Japanese population, where the epidemiology of infectious and noninfectious uveitis and relative incidence of the pathogens are different from other populations. There was variability in how much of the initial pathogen was collected as part of ocular fluid sampling. Furthermore, the presence of this pathogen in the fluid does not prove that it is the causative agent of the inflammation, so even with validation of the test, the utility of this information for the clinician may be limited when deciding on the treatment approach.
Clinical significance
Strip PCR may be beneficial for clinicians as it utilizes a smaller sample size for a given number of pathogens, as opposed to a larger amount of ocular fluid necessary for separate qPCR tests. The results are available in as little as 90 minutes, and the test can be performed by laboratory technicians with minimal training who might otherwise not have access to qPCR. The high sensitivity of the test for viral pathogens, including CMV, HSV1, HSV2, allows for rapid treatment decisions, especially when there is concern for sight-threatening conditions such as viral retinitis. It is also useful when such etiologies need to be excluded prior to starting corticosteroids. Additional real-world validation of the test in other populations will be helpful.