Paper strip test can identify flu subtypes, may have other applications, scientists say

Influenza Variants
Influenza, General
About to perform nasal swab

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A newly developed paper test strip can detect different influenza types and may be able to be identify avian and swine flu strains, potentially guiding both clinical care and disease surveillance efforts, according to a study published in the Journal of Molecular Diagnostics.

Researchers from Princeton University and the Broad Institute of the Massachusetts Institute of Technology and Harvard University collaborated with the US Centers for Disease Control and Prevention on the project. 

The inexpensive, one-step test strip uses CRISPR gene-editing technology to distinguish between influenza A and B and subtypes H1N1 and H3N2. With further development, the test strip could be reprogrammed to distinguish between SARS-CoV-2 and flu and recognize swine flu and avian flu, including the H5N1 subtype currently causing an outbreak in US dairy cattle, the study authors said. 

The team tested the strip using 20 nasal swabs from people with flu-like symptoms during the 2020-2021 flu season, nasal fluid from healthy people as the control, and 2016-2021 influenza sequences downloaded from the National Center for Biotechnology Information Influenza database. They compared the results with those from quantitative reverse transcription-polymerase chain reaction (RT-PCR) tests.

High hopes for point-of-care testing

Paper strip test results of nasopharyngeal samples showed 100% agreement with those of the more expensive and resource- and time-intensive RT-PCR tests. The test can identify two target viruses at the same time, which can help distinguish between flu strains susceptible or resistant to the antiviral drug oseltamivir (Tamiflu). 

Ultimately, we hope these tests will be as simple as rapid antigen tests, and they’ll still have the specificity and performance of a nucleic acid test that would normally be done in a laboratory setting.

Cameron Myhrvold, PhD 

The test was developed in the Harvard lab of co-senior author Pardis Sabeti, MD, DPhil, in 2020 using a technology called Streamlined Highlighting of Infections to Navigate Epidemics (SHINE), which uses CRISPR enzymes to delineate genetic sequences in viral RNA samples. While the researchers initially used SHINE for identification of SARS-CoV-2 and tell apart the virus's Delta and Omicron variants. In 2022, the team altered the test to identify flu viruses.

"Using a paper strip readout instead of expensive fluorescence machinery is a big advancement, not only in terms of clinical care but also for epidemiological surveillance purposes," co-first author Ben Zhang, a Harvard medical student, said in a Broad Institute press release. 

With refinement, the test could be done in 90 minutes at point-of-care sites without the need for specially trained staff, and the researchers said they hope to pare the time needed to 15 minutes. "Ultimately, we hope these tests will be as simple as rapid antigen tests, and they’ll still have the specificity and performance of a nucleic acid test that would normally be done in a laboratory setting," co-senior author Cameron Myhrvold, PhD, of Princeton University, said in the release.

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