Influenza: Underestimated in Children Below 2 Years of Age.

Children under 2 years of age may receive antiviral therapy when influenza is suspected. Signs of influenza are frequently unclear and testing is indicated. The aim of the study was to assess the usefulness of clinical signs and the rapid influenza diagnostic test (RIDT) in diagnosing influenza and in choosing the appropriate treatment. In the 2015-2016 influenza season, 89 children under 2 years of age (56.7% of 157 children diagnosed with influenza) were hospitalized. There were 74 RIDT and 70 reverse transcription polymerase chain reactions (RT-PCR) performed for the purpose of diagnosis, either test per child. Eighty-three percent of children (74/89) presented with fever, 55.1% (49/89) with cough, and 39.3% (35/89) with both cough and fever. The RIDT was positive in 31.1% (23/74) of cases. The highest percentage of positive RIDT was within the first 24 h of disease, decreasing dramatically thereafter (70% vs. 13-17%, respectively). The RIDT shortened the time to diagnosis by 43.8 h/patient (an average €149 gain in treatment costs). The mean delay for RT-PCR-based diagnosis was 33.5 h/patient (an average €114 loss in treatment costs). We conclude that clinical signs have a low diagnostic sensitivity in children under 2 years of age. Likewise, RIDT is of low sensitivity, being diagnostically useful only in the first 24 h. The PCR is recommended for the diagnosis, but that requires a constant access to the method.