A rapid bedside diagnostic test for influenza showed consistent sensitivity and specificity across four consecutive flu seasons in a single pediatric ED in France, according to a report in Diagnostic Microbiology and Infectious Disease.

During flu seasons, it is difficult to distinguish young children who have the flu from those who have serious bacterial infections because clinical symptoms alone cannot differentiate the two conditions and fever may be the only symptom during the onset of a bacterial infection. Rapid influenza diagnostic tests purport to help ED clinicians estimate the probability of influenza at the bedside, which in turn can reduce the need for further diagnostic testing, length of ED stay, inappropriate use of antibiotics, and the costs of care, said Dr. E. Avril of the pediatric ED, University Hospital in Nantes, France, and associates.

To assess the diagnostic value of one rapid influenza diagnostic test used in this setting every winter, the investigators studied 764 patients younger than age 5 years who were admitted to the ED during four consecutive flu seasons with fever of no known origin. The prevalence of influenza varied widely during the study period, from a low of 30% to a high of 62%.

The rapid diagnostic test performed comparably well across the four flu seasons, with only a modest decrease in sensitivity and specificity during the 2010 H1N1 flu pandemic. The bedside test had an overall sensitivity of 0.82, a specificity of 0.98, a positive likelihood ratio of 37.8, and a negative likelihood ratio of 0.19. These results are similar to those of two previous small-scale studies that found sensitivities of 69%-85% and specificities of 83%-98%, Dr. Avril and associates said ( Diag Microbiol Infect Dis. 2016 doi:10.1016/j.diagmicrobio.2016.03.015 ).

These findings “support the rational use of rapid influenza diagnostic tests in clinical practice for young children presenting with fever without a source during flu season,” the investigators said.

Dr. Avril and associates added that they assessed only one rapid diagnostic test for influenza (QuickVue) – the only one available in their ED because of cost – but that there are 22 such tests commercially available. Nantes University Hospital supported the study. Dr. Avril and associates reported having no relevant disclosures.