Table 3.
Pertussis incidence among infants aged younger than 1 year, stratified by month of age, in Yiwu, Zhejiang province, from 1 June 2021 to 31 May 2022.
| Age Group | Eip, n | Eop, n | Mcs, % | Epc, n | Resident Population, N | Ip (95% CrI a) |
|---|---|---|---|---|---|---|
| <3 m | 13.2 | 7.7 | 100.0 | 20.9 | 3836 | 544.8 (434.9–690.0) |
| 3 m | 5.8 | 3.7 | 100.0 | 9.4 | 1151 | 816.7 (571.5–1081.4) |
| 4 m | 7.3 | 6.6 | 100.0 | 13.8 | 1141 | 1209.5 (841.5–1636.5) |
| 5 m | 3.6 | 8.3 | 100.0 | 12.0 | 1159 | 1035.4 (359.2–1729.4) |
| 6–11 m | 0.0 | 39.2 | 100.0 | 39.2 | 6451 | 607.7 (125.1–1102.5) |
| All groups | 29.6 | 84.8 | 100.0 | 114.4 | 13,738 | 832.7 (614.9–1059.4) |
a Calculated by the bootstrap method, the calculation involved the 95% CrI of hospitalization coverage preference rates of SHs, the 95% CrI of the positive rate of enrolled outpatient suspected pertussis cases, the 95% CrI of the medical consultation coverage preference rates of SHs, and the 95% CrI of the medical consultation rates of survey-identified suspected pertussis cases (all shown in the online resources). Eip, estimated inpatient pertussis cases in all hospitals of Yiwu, calculated with Formula (4) in Section 2.4; Eop, estimated outpatient pertussis cases in all hospitals of Yiwu, calculated with Formulas (5) and (6) in Section 2.4; Mcs, medical consultation rate of survey-identified suspected pertussis cases; since only 15 survey-identified suspected pertussis cases were under 1 year of age, the medical consultation rate for infants under 1 year of age (100.0%) was used as a reference for the medical consultation rate of infants at different months of age; Epc, estimated pertussis cases in community of Yiwu, calculated with Formula (7) in Section 2.5; Ip, pertussis incidence per 100,000 person-years, calculated with Formula (8) in Section 2.5; CrI, confidence interval; n, the number of Eip/Eop/Epc; N, the number of resident population; y, year.