# An alternative method for SARS-CoV-2 detection with use modified fluorescent in situ hybridization

## TL;DR

This study presents a new FISH-based method for detecting SARS-CoV-2 that shows higher positivity than standard rRT-PCR tests.

## Contribution

A novel FISH method with a universal probe and specific oligonucleotides for SARS-CoV-2 detection is developed and validated.

## Key findings

- The FISH method detected more positive cases (220) compared to rRT-PCR (200) in 290 samples.
- The difference in results between FISH and rRT-PCR was statistically significant (p = 0.008).
- FISH was successfully standardized on Vero CCL-81 cells and validated on clinical samples.

## Abstract

The real-time reverse-transcriptase polymerase-chain-reaction (rRT-PCR) tests are the gold standard in detecting SARS-CoV-2 virus infection. However, despite high sensitivity and specificity, they have limitations that in some cases may result in false negative results. Therefore, it is reasonable to search for additional tools that could support microbiological diagnosis of SARS-CoV-2. The aim of the study was to develop a highly specific molecular test capable of detecting and visualizing SARS-CoV-2 infection. A universal probe and a set of 18 specific oligonucleotides with a FLAP sequence attached to them on both sides were designed to visualize SARS-CoV-2 virus infection based on the fluorescence in situ hybridization method (FISH). FISH conditions using the developed kit were standardized on the Vero CCL-81 cell line infected by SARS-CoV-2 virus. The method was tested on 290 nasopharyngeal swabs (collected in a doublet) from patients with clinical symptoms of SARS-CoV-2. Each one swab from the doublet was subjected to RNA isolation and amplification by rRT-PCR. From the second swab, a microscopic preparation was performed for FISH. The use of the rRT-PCR allowed obtaining 200 positive and 90 negative results, while our FISH method allowed for 220 positive results and 70 negative results. The differences obtained using both methods were statistically significant (p = 0.008). The obtained results support the use of FISH as an additional method in microbiological diagnostics of SARS-CoV-2.