TABLE 1. Influenza acute respiratory or febrile illness hospitalization rate and dominant influenza viruses among pregnant or postpartum women* — Suzhou, China, 2018–2023.
| Metric | Analysis period |
|||||
|---|---|---|---|---|---|---|
| Oct 2018–Sep 2019 | Oct 2019–Sep 2020 | Oct 2020–Sep 2021 | Oct 2021–Sep 2022 | Oct 2022–Sep 2023 | Overall | |
| No. of ARFI hospitalizations |
965 |
570 |
431 |
464 |
899 |
3,329
|
| No. of live births |
68,487 |
61,916 |
66,068 |
53,296 |
49,724 |
299,491
|
| Annual ARFI hospitalizations per 1,000 live births (95% CI) |
14.1
(13.2–15.0) |
9.2
(8.5–10.0) |
6.5
(5.9–7.2) |
8.7
(7.9–9.5) |
18.1
(16.9–19.3) |
11.1
(10.7–11.5)
|
| No. of sampled and tested ARFI hospitalizations (%) |
878
(91.0) |
526
(92.3) |
417
(96.8) |
452
(97.4) |
860
(95.7) |
3,133
(94.1)
|
| No. of influenza ARFI hospitalizations (%) |
233
(26.5) |
99
(18.8) |
3
(0.7) |
77
(17.0) |
83
(9.7) |
495
(15.8)
|
| Annual influenza ARFI hospitalizations per 1,000 live births (95% CI) |
3.4
(3.0–3.9) |
1.6
(1.3–2.0) |
0.05
(0.01–0.13) |
1.4
(1.1–1.8) |
1.7
(1.3–2.1) |
2.1
(1.9–2.3)†
|
| Estimated total annual ARFI cases per 1,000 live births (95% CI)§,¶ |
440.3
(303.7–933.9) |
287.8
(196.7–616.9) |
203.8
(141.1–440.3) |
272.2
(188.7–589.4) |
565.0
(391.4–1,204.7) |
347.5
(240.3–731.5)
|
| Estimated total annual influenza ARFI cases per 1,000 live births (95% CI)§,¶ |
106.3
(72.6–236.3) |
50.0
(33.4–116.4) |
1.6
(0.5–7.2) |
45.0
(29.4–107.8) |
52.2
(34.3–123.3) |
65.9
(45.2–142.4)†
|
| Dominant influenza viruses** | A(H1N1)pdm09 | B/Victoria | B/Victoria | A(H3N2) and B/Victoria | A(H1N1)pdm09 and A(H3N2) | A(H1N1)pdm09, A(H3N2), and B/Victoria |
Abbreviations: ARFI = acute respiratory or febrile illness; influenza ARFI = laboratory-confirmed influenza-associated acute respiratory or febrile illness.
* <2 weeks postpartum.
† Because influenza activity during 2020–21 did not achieve epidemic levels, these data were excluded from the calculation of the average. The start of each influenza epidemic period was defined as the first day of 3 consecutive influenza reporting weeks in which the percentage of specimens testing positive for any influenza virus infection exceeded 5%. The end of each influenza epidemic period was defined as the day before the first of 3 consecutive influenza reporting weeks during which the percentage of specimens testing positive for influenza was <5%.
§ The total annual ARFI or influenza ARFI rates were estimated through observed hospitalization rates divided by the percentage of hospitalizations among the total number of pregnant or postpartum women with ARFI or influenza ARFI. The percentages of hospitalizations among the total number of pregnant or postpartum women with ARFI or influenza ARFI were assumed the same and equal to the percentage of hospitalizations among the total number of pregnant or postpartum women with influenza (3.2%; 95% CI = 1.5%–4.9%). https://pubmed.ncbi.nlm.nih.gov/34323381
¶ Including cases that were and were not medically attended, outpatients, and inpatients.
** Dominant influenza viruses were defined as those 1) accounting for ≥70% of all isolates during the season or 2) accounting for 40%–70% of all isolates, and the second most common virus accounted for <30%. Subtype/lineage was considered as codominant with the most common virus if it accounted for ≥30% of all isolates.