A straightforward test of human immune responses can show whether flu-like symptoms arise from bacterial or viral infection.

A team led by Christopher Woods and Geoffrey Ginsburg of Duke University in Durham, North Carolina, developed an assay based on a technique called RT-PCR, which can measure gene expression in blood samples.

The assay monitors roughly 30 human genes that have differing activities in bacterial and viral infections. When used on 102 people who came to a hospital with fevers and respiratory symptoms, the test identified a viral infection with 94% accuracy and could exclude a viral cause with 89% accuracy.

Sci. Transl. Med. 5, 203ra126 (2013)