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PostPosted: Tue Dec 29, 2009 7:54 pm 
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http://www.genomeweb.com/pcrsample-prep ... h1n1-tests

Studies Suggest Viral Variants Confound PCR-based Influenza A, H1N1 Tests

Using real-time reverse transcriptase PCR to detect influenza A and its subtypes may be more complicated than previously thought, according to two papers published online ahead of print this week in the Journal of Clinical Microbiology.

One study, led by Xiaotian Zheng at Children's Memorial Hospital in Chicago, describes the discovery of a variant of the 2009 H1N1 influenza virus that the ProFlu+ test marketed by Gen-Probe's Prodesse business failed to flag as positive for influenza A.

The other study, led by Bobbi Pritt at the Mayo Clinic, found an "unexpected" amount of mutability in the matrix gene of the 2009 H1N1 virus, which led to "loss of viral subtype discriminatory ability using [rRT-PCR-based melting temperature] analysis within just three months of the pandemic."

Currently, rRT-PCR-based influenza tests are considered the gold standard for flu screening. The US Centers for Disease Control and Prevention has recommended rRT-PCR-based tests over rapid antigen testing for 2009 H1N1, largely because the antigen-based tests pose a higher risk of false negatives.

The recent findings published in JCM, however, indicate that clinicians may need to take a bit more care when interpreting the results of rRT-PCR-based tests.

"Our rules are that we treat the PCR results as final, or more or less confirmed," Zheng told PCR Insider. "They overrule all other results, including rapid tests, which are known to be much less accurate than culture or PCR."

Nevertheless, his team's work "underscores the need for cautious interpretation and additional testing when a negative RT-PCR result does not seem to fit clinical presentation," according to the paper.

ProFlu+ Discrepancy

Zheng's study, conducted in collaboration with researchers from the Cleveland Clinic, Evanston Hospital, and Gen-Probe's Prodesse group, was sparked when a sample from a 4-year-old girl tested "strongly positive" for influenza A on a rapid antigen test, but negative on the ProFlu+ test, an assay cleared by the Food and Drug Administration to detect and differentiate influenzas A and B and respiratory syncytial virus.

After two other rapid antigen tests yielded positive results, the researchers ran the girl's sample on Prodesse's ProFlu-ST — a sub-typing rRT-PCR test that differentiates the 2009 H1N1, seasonal H1, and seasonal H3 viruses — and found that the sample was positive for 2009 H1N1.



.... continues at link .....


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PostPosted: Tue Dec 29, 2009 10:01 pm 
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Joined: Sat Dec 12, 2009 8:43 pm
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Isn't this precisely what littlebird has been complaining about? Tests that don't work. If so, it's good to see it being recognized.


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PostPosted: Wed Dec 30, 2009 12:20 am 
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Joined: Tue Nov 24, 2009 7:10 pm
Posts: 399
If the reports from Egypt and Vietnam and others continue to integrate into the populations,

How long will it take to be seen, and will it be seen in fatal cases escalating? And what test are they using to define H5N1?


Of the 90 laboratory confirmed cases of Avian influenza A(H5N1) reported in Egypt, 27 have been fatal.

Of the 112 cases confirmed to date in Viet Nam, 57 have been fatal.


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