Detection of influenza C viruses among outpatients and patients hospitalized for severe acute respiratory infection, Minnesota, 2013–2016

Thielen, Beth K.; Friedlander, Hannah; Bistodeau, Sarah; Shu, Bo; Lynch, Brian; Martin, Karen; Bye, Erica; Como-Sabetti, Kathyrn; Boxrud, David; Strain, Anna K.; Chaves, Sandra S.; Steffens, Andrea; Fowlkes, Ashley L.; Lindstrom, Stephen; Lynfield, Ruth

BACKGROUND: Existing literature suggests that influenza C typically causes mild respiratory tract disease. However, clinical and epidemiological data are limited. METHODS: Four outpatient clinics and three hospitals submitted clinical data and respiratory specimens through a surveillance network for acute respiratory infection (ARI) during May 2013 through December 2016. Specimens were tested using multi-target nucleic acid amplification tests (NAAT) for 19–22 respiratory pathogens, including influenza C. RESULTS: Influenza C virus was detected among 59 of 10,202 (0.58%) hospitalized SARI cases and 11 of 2,282 (0.48%) outpatients. Most detections occurred from December to March, with 73% during the 2014–2015 season. Influenza C detections occurred among patients of all ages, with similar rates between inpatients and outpatients. The highest rate of detection occurred among children aged 6 to 24 months (1.2%). Among hospitalized cases, seven required intensive care. Medical co-morbidities were reported in 58% of hospitalized cases and all who required intensive care. At least one other respiratory pathogen was detected in 40 (66%) cases, most commonly rhinovirus/enterovirus (25%) and respiratory syncytial virus (RSV) (20%). The hemagglutinin-esterase-fusion (HEF) gene was sequenced in 37 specimens, and both C/Kanagawa and C/Sao Paulo lineages were detected in inpatients and outpatients. CONCLUSIONS: We found seasonal circulation of influenza C with year-to-year variability. Detection was most frequent among young children, but occurred in all ages. Some cases positive for influenza C, particularly those with co-morbid conditions, had severe disease, suggesting a need for further study of the role of influenza C virus in the pathogenesis of respiratory disease.