Does serum alpha interferon measurement aid in the etiological diagnosis of febrile adult patients?

In febrile patients, distinguishing bacterial from viral infections is crucial for early treatment initiation and rational use of antibiotics. Raised interferon-alpha (IFN-alpha) levels in serum has been associated with a wide range of viral infections. We evaluated the effectiveness of IFN-alpha serum measurements for the etiological diagnosis of febrile patients. Adult patients who were attending the emergency department with body temperature above or equal to 38.5 degrees C were studied prospectively, followed-up until day 30, and classified by two independent experts (blind for IFN-alpha results) as having a bacterial/parasitic infection, viral infection, or other diagnosis. The results of IFN-alpha measurements in blood samples taken in the emergency room, were compared with expert diagnosis. Among 243 patients included, 167 had bacterial/parasitic infections (including 19 with viral co-infection), 59 had viral infections, and 36 other diagnoses. IFN-alpha assay had a sensitivity of 0.44 and a specificity of 0.92 for the diagnosis of viral infection. Among the 20 patients with acute viral infection according to the emergency physician diagnosis, 7 (35%) were given antibiotics, including four patients with raised IFN-alpha concentrations. It is concluded that in febrile patients, raised serum IFN-alpha level is highly specific of the viral etiology of fever but poorly sensitive. Reliable viral and bacterial biological markers are needed in order to improve rational use of antibiotics.