Tuesday, August 16, 2011

Viral or Bacterial Infection? A Blood Test

This is another "someday, in the future" article that made the rounds with the news releases yesterday - where, supposedly, within a few hours of infection, there are significant differences in phagocyte chemiluminescence that allow researchers to differentiate between viral and bacterial infections.

As usual, the breathless commentary is a little ahead of the actual research results.  What the authors did was a data-mining experiment from 69 patients, each of whom had been diagnosed (through standard clinical practice) with either a viral infection, or a bacterial infection.  They ran all the polymorphonuclear leukocytes through their assay, recorded several different sorts of chemoluminescence, and then let computer software do a partitioning analysis to determine the most predictive patterns for bacterial and viral infections.

The software trained to 94.7% accuracy on the "knowns", and then, when tested on a confusion sample with 18 "unknowns" it was 88.9% accurate.

So, still not good enough for clinical use as a dichotomous result, but if it were allowed to return an equivocal range that quantified the assay uncertainty, then perhaps it could have a role in clinical practice.  In theory, an assay such as this might otherwise reduce additional testing and help reduce the number of viral infections that receive antibiotics.

"Differentiation Between Viral and Bacterial Acute Infectious Using Chemiluminescent Signatures of Circulating Phagocytes"
http://www.ncbi.nlm.nih.gov/pubmed/21517122

2 comments:

  1. This may be a little late for clinical medicine...it is already becoming clear that many of the infections we know to be bacterial - Strep throat specifically and probably otitis media and bronchitis (usually viral but bacterial often enough) - don't really need to be treated with antibiotics anyway. Notwithstanding the recent NEJM article to the contrary re: Otitis Media (Secondary endpoints!!)

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  2. The way I envisioned this test mostly would be to ideally reduce antibiotic usage for commonly diagnosed conditions that are frequently viral but usually treated as bacterial - such as otitis media or pediatric pneumonias.

    Now, whether OM/strep/bronchitis/sinusitis derives any benefit from antibiotics is an entirely separate debate. There is clearly a subset of OM/bronchitis/sinusitis that is bacterial and may benefit from antibiotics, but there usually aren't any useful identifying clinical criteria that differentiate that group. Unilateral purulent nasal discharge seemed to be predictive for sinusitis in the large, retrospective analyzes, nothing helps with OM, and the only group that seems to benefit from antibiotics for bronchitis is in the elderly to prevent subsequent pneumonia. For strep, the NNT to prevent peritonsillar abscess is on the order of 4000, while the NNT (in the U.S.) to prevent rheumatic fever is probably at least 100,000.

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