Epidemiological information regarding the periodic epidemics of influenza C virus in Japan (1996-2013) and the seroprevalence of antibodies to different antigenic groups.

BACKGROUND

Although influenza C virus is widely distributed throughout the world, epidemiological information, based on long-term surveillance, has not yet been acquired.

OBJECTIVES

To clarify the epidemiological features of influenza C virus infection, and to examine whether the prevalence of the antibodies against the influenza C virus is associated with the epidemics.

STUDY DESIGN

Between 1996 and 2013, 36,973 respiratory specimens were collected from two pediatric outpatient clinics in Yamagata, Japan. The specimens were examined for the presence of influenza C virus using cell culture methods. Isolated viruses were antigenically analyzed. The differences in seropositivity, with respect to the different antigenic groups, were examined using serum samples collected in 2001 and 2011 by a hemagglutination inhibition assay.

RESULTS

Influenza C viruses were isolated from 190 specimens during an 18-year period. Most influenza C viruses were isolated from winter to early summer in even-numbered years, and the frequency of virus isolation per year ranged from 0.43% to 1.73%. An antigenic analysis revealed that the dominant antigenic groups were the C/Yamagata/26/81 from 1996 to 2000, the C/Kanagawa/1/76 in 2002 and 2004, and the C/Sao Paulo/378/82 from 2006 to 2012. When compared to the other antigenic groups, the seroprevalence of the C/Sao Paulo/378/82 group was lower in 2001 for individuals older than 5 years and was higher in 2011 in individuals younger than 40 years.

CONCLUSIONS

The results from our study suggest that epidemics of influenza C virus infection periodically occur and the replacement of the dominant antigenic group may be caused by immune selection within older children and/or adults in the community.