Correlation analysis between positivity rate of immunoglobulin G antibodies against pertussis toxin among community-based populations and reported pertussis incidence in Shandong, China: A seven-year seroepidemiological study

Abstract

Background The reported annual incidence of pertussis in China has shown a marked increase over the past decade, but it may be still underestimated. The purpose of this study was to understand the seroepidemiologic characteristics of pertussis in community-based populations and to assess the level of pertussis infection in the population. Methods Between 2017 and 2023, one or two cities in each of the eastern, central and western regions of Shandong Province were selected as survey sites, and a total of six age groups of healthy individuals were enrolled by multistage stratified random sampling to carry out the survey. The serum level of pertussis toxin (PT) IgG (PT-IgG) antibody was quantified by indirect enzyme-linked immunosorbent assay. Results A total of 9,238 subjects were enrolled, and the mean positive rate of PT-IgG antibody was 8.05% (95%CI: 7.50%~8.60%), with the highest in 2019 (10.70%, 95% CI: 9.19%~12.21%) and the lowest in 2020 (6.32%, 95% CI: 4.98%~7.66%). The highest positive rate was found in the age group of less than 3 years old (11.46%, 95%CI: 9.87%~13.05%), and the lowest rate was found in the 3 ~ 5 years group (5.40%, 95%CI: 4.28%~6.52%). There was a significant difference in the positive rate between age groups (χ² = 43.098, P < 0.001). Comparison of trends in recent infection rates and reported incidence rates in the population, that showed a very strong linear correlation in the annual distribution (r = 0.821, P = 0.023), and a extremely weak linear correlation in age distribution (r = 0.086, P = 0.872). Estimated infection rates (/100,000) among people aged ≥ 3 years ranged from 5,257 (95%CI: 3,918 ~ 6,596) to 24,449 (95%CI: 22,157 ~ 26,740) by years, with estimated infection rates in eastern region (31,544.44-fold) and in older age group (292,340.00-fold for ≥ 20 years old group, 216,388.89-fold for 17 ~ 19 years old group) differed significantly from the reported incidence rate. Conclusions The annual distribution trend of reported pertussis incidence rate aligns with the infection rate observed among community populations, the actual level of infection is likely to be seriously underestimated. Therefore there is a need to emphasize surveillance and consider additional booster immunizations for adolescents and adults.