Some hospitalized children with acute bronchiolitis (AB) and febrile seizures (FB) present with influenza C virus (ICV), which may contribute to more severe clinical presentations, particularly in those with AB, a recent study in Slovenia has found.
“Even though the overall prevalence was low, the absence of ICV in healthy controls and its detection as a mono-infection in some cases support a possible role in paediatric respiratory and febrile illness,” the investigators said.
ICV was found in 4 out of 307 (1.3 percent) children with AB and five out of 192 (2.6 percent) with FS, but not among healthy control participants. More than half (5/9 cases, 56 percent) of those who tested positive for ICV had coinfections, while ICV was the only virus detected in one child with AB and three with FS. [Pediatr Infec Dis J 2026;45:432-436]
“Interestingly, ICV was more frequently detected among children with FS than those with AB,” the investigators said. “Among ICV-positive cases, some were coinfected with other respiratory viruses, whereas others had ICV as the only pathogen detected.”
Such finding “supports previous observations that ICV often cocirculates with other respiratory viruses, making it difficult to determine its independent pathogenic role,” they added. [Viruses 2020;12:89; J Infect Dis 2006;193:1229-1235; Clin Infect Dis 2018;66:1092-1098]
Notably, ICV positivity appeared to lead to a more severe disease among children with AB, including one that required oxygen therapy for 5 days.
In phylogenetic analysis, all Slovenian ICV strains belonged to clade I, closely related to the Yamagata lineage, according to the investigators.
Routine diagnosis
Unfortunately, ICV is not part of the standard respiratory virus diagnostic panels, and such omission may result in a missed etiological diagnosis, as shown by the AB case with no other identified pathogen.
“Given that ICV is not included in routine diagnostic panels, its role as an underrecognized respiratory pathogen deserves further investigation,” the investigators said. “Additional testing should be considered in children hospitalized for respiratory illness with negative results for common respiratory viruses.”
Furthermore, two children with mono-infections (one with AB and one with FS) experienced diarrhoea, suggesting a potential gastrointestinal manifestation, albeit rare.
These findings are consistent with previous studies reporting cases involving influenza A and B viruses and showing an association with more severe illnesses. [J Pediatr 1991;118:235-238; J Forensic Sci 2008;53:213-215; Lancet 1975;1:291-295; N Engl J Med 2005;353:2559-2567]
“Although the low number of ICV-positive cases precludes definitive conclusions regarding seasonality, our data suggest higher circulation during the fall and spring months—consistent with prior reports,” the investigators said. [J Med Virol 2008;80:1441-1446; Diagn Microbiol Infect Dis 2011;69:419-427]
The current study analysed 499 nasopharyngeal swabs collected from children up to 6 years of age at the University Medical Center Ljubljana, Ljubljana, Slovenia, between October 2009 and September 2011. Participants included 307 children with AB, 192 with FS, and 150 healthy controls.
The investigators used RT-PCR to detect respiratory viruses, including ICV. They further analysed ICV-positive samples by Sanger sequencing and phylogenetic analysis.
“Longitudinal studies and expanded molecular surveillance are needed to better define the clinical and epidemiological impact of ICV,” the investigators said.