[Seroepidemiology of pertussis in healthy population in Ningbo, 2019]

Objective: To understand the seroepidemiological characteristics of pertussis in healthy population in Ningbo, and estimate the overall incidence of pertussis. Methods: A cross-sectional survey method was used in this study. A total of 1 206 healthy residents in 9 age groups were stratified randomly selected from 3 counties of Ningbo. Serum samples were collected from the subjects, and the pertussis toxin immunoglobulin G antibody (PT-IgG) levels were measured quantitatively by enzyme-linked immunosorbent assay (ELISA). Results: The mean PT-IgG seropositive rate in the subjects was 0.91% (95%CI:0.45%-1.63%) with a geometric mean titer (GMT) of 3.10 (95%CI:2.86-3.36) IU/ml. The seropositive rates ranged from 0.00% to 1.68%, and the GMTs ranged from 2.08 IU/ml to 5.28 IU/ml in 9 age groups. The incidence rate of pertussis was estimated to be 4 572.81 per 100 000 in age group ≥5 years (95%CI:1 807.30 per 100 000-9 348.12 per 100 000), and the peak of estimated incidence rates were found in age group 5- years (9 301.62 per 100 000, 95%CI:1 121.77 per 100 000-33 154.68 per 100 000) and age group ≥50 years old (8 967.02 per 100 000, 95%CI: 1 059.45 per 100 000-31 845.94 per 100 000). Conclusions: The actual incidence of pertussis was high in Ningbo in 2019. As a result of waning immunity after vaccination, pertussis can occur in adolescents and adults. The pertussis surveillance should be strengthened and the pertussis vaccination strategy should be improved.