Influenza C generally isn´t thought to be a cause clinically significant disease, but a study in Italian children who were seen in the emergency department for pneumonia found the virus in five children, with a disease severity that resembled influenza A.

The study evaluated data from four flu seasons from 2008-09 to 2011-12 at a pediatric clinic in Milan and appeared today in an early online edition of Influenza and Other Respiratory Viruses.

Influenza C can infect humans and pigs, and infections are rare compared with influenza A and B.

The researchers included healthy children from ages 1 month to 14 years who were seen because of fever and lower respiratory tract symptoms and whose chest radiographs suggested community-acquired pneumonia. Respiratory swabs and sera were collected, and researchers noted patients´ clinical information and whether each child was hospitalized.

Respiratory samples were tested for influenza A, B, and C, and the samples that tested positive were tested for several other viral coinfections. Researchers sequenced the positive influenza C samples to determine the lineage.

Of 391 children included in the study, influenza C was identified in 5 (1.3%). Influenza A was detected in 26 children, and influenza B was found in 3. Influenza C was found only during two of the four seasons: 2008-09 and 2009-10.

Four of the children with influenza C were younger than 3 years old, and one was 14 years old. No viral coinfections were found in the children who had influenza C.

All of the children with influenza C infections were hospitalized, but their clinical symptoms improved a few days later. Researchers observed that the severity of influenza C symptoms was similar to those for influenza A, but worse than in kids with pneumonia related to influenza B. All children with influenza C pneumonia recovered with no disease recurrence, according to the study.

Phylogenetic analysis showed that the five influenza C viruses clustered in two of the six lineages: Kanagawa/1/76 and Sao Paulo/378/82.

The group wrote that the study is the first that they know of that gauges the importance of influenza C in pediatric community-acquired pneumonia. However, they noted that further study is needed to determine what role influenza C plays during other parts of the year, given that previous studies have shown that the virus doesn´t have the same seasonal pattern as the other two flu types.

Though the similar clinical pictures between influenza A and influenza C have been found in other studies, the role of influenza C is notable, especially since it can be an important cause of community-acquired pneumonia in kids, the authors write.

The findings of the study have parallels to a 2006 study on hospitalized Spanish infants conducted from September 1999 through July 2003, which found influenza C infections in six of 706 children.

Three of the six, however, had viral coinfections, and the earlier study did not focus exclusively on community-acquired pneumonia. As with the Italian study, though, the influenza C infections in the Spanish study were clinically similar to influenza A infections.

Principi N, Scala A, Daleno C, et al. Influenza C virus-associated community-acquired pneumonia in children. Influenza Other Respi Viruses 2012 Dec 7 [Abstract]

See also:

October 2006 Emerg Infect Dis letter