A cross sectional survey measuring sero-incidence of pertussis infection among Japanese junior and senior high school students in 2013 and 2014

Regression analysis showed an average decrease of 35% in IgG PT between 2013 and 2014. In 2013, 4.4% of the students showed IgG PT levels ≥100 EU/mL, as did 3.7% in 2014. The seroincidence, defined as [IgG PT] change from <100 in 2013 to ≥100 EU/mL in 2014, was 10.3 cases per 1000 person-years. A 4-fold rise in IgG PT was seen in 2.1% of the students, with significant differences between schools and significant correlations to two risk factors, “over 2 weeks coughing” and “exposure to a person with over 2 weeks coughing”. A substantial number of students had IgG PT ≥100 EU/mL despite the observed 35% yearly decrease in IgG PT level. The local foci of ≥4-fold IgG PT increase in specific schools suggests the persistent circulation of B. pertussis in Japanese adolescents. The results also support a “≥4-fold rise in IgG PT” as a useful component of the sero-epidemiological surveillance for pertussis.