Influenza C: A Common Cause of URT Illness

In children younger than 6 years but older than 6 months, the influenza C virus is a significant cause of upper respiratory tract illness and is probably contracted in many cases from a preschool-aged child in the same home, Japanese researchers reported.

Dr. Yoko Matsuzaki of the department of infectious diseases at Yamagata (Japan) University and colleagues developed a tissue-culture method to test for the virus, and then examined roughly 85,000 respiratory tract specimens collected over a 14-year period from asymptomatic children who were no older than 15 years and had been seen at any of seven Japanese pediatric clinics and hospitals. In total, 187 specimens (0.22%) were positive for influenza C; 17 were excluded because of respiratory coinfection or incomplete medical records. The investigators obtained clinical data on the 170 remaining children and performed nucleotide sequencing to look at intrafamily transmission (J. Infect. Dis. 2006;193:1229–35).

There was a strong association between influenza C upper respiratory tract (URT) infection and the preschool age range. Indeed, 92% of the children found to have influenza C virus were between 6 months and 6 years old—a fact likely explained, they noted, by prior studies' findings that most humans acquire antibodies to influenza C by age 7–10 years and that newborns receive maternal antibodies against the virus that vanish by 6 months—leaving an open window of virus vulnerability in the intervening age group.

In the study, the infection incidence among 1-year-old children was more than three times that of children aged 7–12 months. Although only 17% of the total were hospitalized, this rate was nearly doubled (30%) in children younger than 2 years. The incidence among girls and boys was similar.

As to the transmission vector, “households are important sites for the transmission of the influenza viruses,” the researchers said—but for influenza C, they noted that “preschool children might play a significant role” in bringing the virus into the home.

Influenza C causes symptoms similar to those of other influenza strains. The most common symptoms in the study were fever, cough, and runny nose. This was true for children both younger and older than 6 years, regardless of whether the child was hospitalized. More than three-fourths (79%) of children who were not hospitalized were diagnosed with upper respiratory tract infection or influenza.

The authors found that most influenza C infections occurred in the winter and spring, but especially in the period from April through June. However, they noted that this seasonal association is not evident in regions of the world that—unlike snowy north central Japan—have mild winters. Thus, wintertime influenza C likely often coexists with influenza A and B in temperate areas, making differential diagnosis important.

In children younger than 6 years but older than 6 months, the influenza C virus is a significant cause of upper respiratory tract illness and is probably contracted in many cases from a preschool-aged child in the same home, Japanese researchers reported.

Dr. Yoko Matsuzaki of the department of infectious diseases at Yamagata (Japan) University and colleagues developed a tissue-culture method to test for the virus, and then examined roughly 85,000 respiratory tract specimens collected over a 14-year period from asymptomatic children who were no older than 15 years and had been seen at any of seven Japanese pediatric clinics and hospitals. In total, 187 specimens (0.22%) were positive for influenza C; 17 were excluded because of respiratory coinfection or incomplete medical records. The investigators obtained clinical data on the 170 remaining children and performed nucleotide sequencing to look at intrafamily transmission (J. Infect. Dis. 2006;193:1229–35).

There was a strong association between influenza C upper respiratory tract (URT) infection and the preschool age range. Indeed, 92% of the children found to have influenza C virus were between 6 months and 6 years old—a fact likely explained, they noted, by prior studies' findings that most humans acquire antibodies to influenza C by age 7–10 years and that newborns receive maternal antibodies against the virus that vanish by 6 months—leaving an open window of virus vulnerability in the intervening age group.

In the study, the infection incidence among 1-year-old children was more than three times that of children aged 7–12 months. Although only 17% of the total were hospitalized, this rate was nearly doubled (30%) in children younger than 2 years. The incidence among girls and boys was similar.

As to the transmission vector, “households are important sites for the transmission of the influenza viruses,” the researchers said—but for influenza C, they noted that “preschool children might play a significant role” in bringing the virus into the home.

Influenza C causes symptoms similar to those of other influenza strains. The most common symptoms in the study were fever, cough, and runny nose. This was true for children both younger and older than 6 years, regardless of whether the child was hospitalized. More than three-fourths (79%) of children who were not hospitalized were diagnosed with upper respiratory tract infection or influenza.

The authors found that most influenza C infections occurred in the winter and spring, but especially in the period from April through June. However, they noted that this seasonal association is not evident in regions of the world that—unlike snowy north central Japan—have mild winters. Thus, wintertime influenza C likely often coexists with influenza A and B in temperate areas, making differential diagnosis important.

In children younger than 6 years but older than 6 months, the influenza C virus is a significant cause of upper respiratory tract illness and is probably contracted in many cases from a preschool-aged child in the same home, Japanese researchers reported.

Dr. Yoko Matsuzaki of the department of infectious diseases at Yamagata (Japan) University and colleagues developed a tissue-culture method to test for the virus, and then examined roughly 85,000 respiratory tract specimens collected over a 14-year period from asymptomatic children who were no older than 15 years and had been seen at any of seven Japanese pediatric clinics and hospitals. In total, 187 specimens (0.22%) were positive for influenza C; 17 were excluded because of respiratory coinfection or incomplete medical records. The investigators obtained clinical data on the 170 remaining children and performed nucleotide sequencing to look at intrafamily transmission (J. Infect. Dis. 2006;193:1229–35).

There was a strong association between influenza C upper respiratory tract (URT) infection and the preschool age range. Indeed, 92% of the children found to have influenza C virus were between 6 months and 6 years old—a fact likely explained, they noted, by prior studies' findings that most humans acquire antibodies to influenza C by age 7–10 years and that newborns receive maternal antibodies against the virus that vanish by 6 months—leaving an open window of virus vulnerability in the intervening age group.

In the study, the infection incidence among 1-year-old children was more than three times that of children aged 7–12 months. Although only 17% of the total were hospitalized, this rate was nearly doubled (30%) in children younger than 2 years. The incidence among girls and boys was similar.

As to the transmission vector, “households are important sites for the transmission of the influenza viruses,” the researchers said—but for influenza C, they noted that “preschool children might play a significant role” in bringing the virus into the home.

Influenza C causes symptoms similar to those of other influenza strains. The most common symptoms in the study were fever, cough, and runny nose. This was true for children both younger and older than 6 years, regardless of whether the child was hospitalized. More than three-fourths (79%) of children who were not hospitalized were diagnosed with upper respiratory tract infection or influenza.

The authors found that most influenza C infections occurred in the winter and spring, but especially in the period from April through June. However, they noted that this seasonal association is not evident in regions of the world that—unlike snowy north central Japan—have mild winters. Thus, wintertime influenza C likely often coexists with influenza A and B in temperate areas, making differential diagnosis important.