Influenza C virus in U.S. children with acute respiratory infection 2016-2019.

Influenza C virus (ICV) is an orthomyxovirus related to influenza A and B, yet due to few commercial assays, epidemiologic studies may underestimate incidence of ICV infection and disease. We describe the epidemiology and characteristics of ICV within the New Vaccine Surveillance Network (NVSN), a Centers for Disease Control and Prevention (CDC)-led network that conducts population-based surveillance for pediatric acute respiratory illness (ARI). Nasal or/combined throat swabs were collected from emergency department (ED) or inpatient ARI cases, or healthy controls, between 12/05/2016-10/31/2019 and tested by molecular assays for ICV and other respiratory viruses. Parent surveys and chart review were used to analyze demographic and clinical characteristics of ICV+ children. Among 19,321 children tested for ICV, 115/17,668 (0.7 %) ARI cases and 8/1653 (0.5 %) healthy controls tested ICV+. Median age of ICV+ patients was 18 months and 88 (71.5 %) were ≤36 months. Among ICV+ ARI patients, 40 % (46/115) were enrolled in the ED, 60 % (69/115) were inpatients, with 15 admitted to intensive care. Most ICV+ ARI patients had fever (67.8 %), cough (94.8 %), or wheezing (60.9 %). Most (60.9 %) ARI cases had ≥1 co-detected viruses including rhinovirus, RSV, and adenovirus. In summary, ICV detection was rarely associated with ARI in children, and most ICV+ patients were ≤3 years old with co-detected respiratory viruses.