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Influenza Type C as a Cause of Pediatric Pneumonia

Amesh A. Adalja, MD, FACP, January 11, 2013

Of the influenza virus types, A and B are of most concern as disease-causing pathogens. Type C has not been paid much attention, but more sophisticated respiratory viral testing is now shedding light on the role of this pathogen in causing disease, particularly in children. A new study by Italian researchers, recently published in Influenza and Other Respiratory Viruses, characterizes the role of influenza C in pediatric pneumonia.1

Distinct Virological Features of Influenza C

Discovered in 1950, type C was the last of the 3 influenza viruses to be discovered. The virus is not seasonal, and it circulates in multiple lineages. Other prominent features include the following:2

  • 7 gene segments (vs. 8 in A and B)
  • 9 viral proteins (vs. 10 in A and 11 in B)
  • Does not infect avian species
  • Does not undergo antigenic shift

Four Flu Seasons Studied

In their recent study, Principi and colleagues included data from the 2008-2012 influenza seasons. The study included 391 patients, who ranged in age from 1 month to 14 years. All had presented to an emergency department with signs and symptoms of a lower respiratory tract infection, and all had chest radiographs consistent with community-acquired pneumonia. PCR testing for influenza A, influenza B, and influenza C was performed on respiratory secretions. Additional testing using a PCR-based respiratory virus panel was used to identify any co-infections with RSV, parainfluenza, coronavirus, adenovirus, hMPV, rhinovirus, and bocavirus. No child was treated with antivirals.

5 Cases of Influenza C Pneumonia

Of the 391 children studied, 5 (1.3%) had influenza C identified in their respiratory secretions. All 5 cases were hospitalized; none had co-infections. Four cases occurred in children under 3 years. All experienced complete cure. Illness was more severe than that in children with influenza B-associated pneumonia.1

More Testing for Influenza C?

One of the most important implications of this study, coupled with earlier reports3,4,5 of influenza C infection, is that wider testing for influenza C may be warranted. Because it is not seasonal, influenza C can be considered a year-round pathogen that may, on a yearly basis, contribute to a substantial burden of illness, hospitalization, and inappropriate antibacterial utilization.

These studies raise other key questions as well: What is the rate of influenza C infection in adults? Does influenza C have transmissibility characteristics similar to those of influenza A and B? Are droplet precautions required as with other influenza viruses? And, finally, are antivirals (oseltamivir and zanamivir) as effective against influenza C as they are against influenza A and B? Does the adamantane class of antivirals have any activity? Further investigation is warranted.


  1. Influenza C virus-associated community-acquired pneumonia in children [published online ahead of print December 7, 2012]. Influenza Other Respi Viruses. 2013;7(1). doi:10.1111/irv.12062

  2. Treanor JJ. Influenza viruses, including avian influenza and swine influenza. In: Mandell GL, Bennett JE, Dolin R, eds. Mandell, Douglas, and Bennett’s Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, PA: Churchill Livingstone; 2010.

  3. Calvo C, Garcia-Garcia ML, Centeno M, et al. Influenza C virus infection in children, Spain. Emerg Infect Dis. 2006;12:1621-1622.

  4. Anton A, Marcos MA, Codoner FM, et al. Influenza C virus surveillance during the first influenza A (H1N1) 2009 pandemic wave in Catalonia, Spain. Diagn Microbiol Infect Dis. 2011;69:41927.

  5. Gourain S, Vabret A, Dina J, et al. Study of influenza C virus infection in France. J Med Virol. 2008;80:1441-1446.