TABLE 2.
Influenza incidence during the epidemic periods a in the annual cohorts of China respiratory illness surveillance among pregnant women (CRISP), Suzhou, 2015/2016–2017/2018 seasons (per 100 person‐months)
| 2015/2016 | 2016/2017 | 2017/2018 | Overall incidence | |||||
|---|---|---|---|---|---|---|---|---|
| Rate (95% CI) | p | Rate (95% CI) | p | Rate (95% CI) | p | Rate (95% CI) | p | |
| ARI influenza by age at enrollment | ||||||||
| <25 y | 0.6 (0.3, 1.0) | REF | 0.8 (0.4, 1.3) | REF | 2.4 (1.6, 3.2) | REF | 1.1 (0.8, 1.5) | REF |
| 25–29y | 0.6 (0.4, 0.8) | 1.000 | 1.1 (0.9, 1.3) | 0.362 | 2.0 (1.6, 2.4) | 0.559 | 1.2 (1.0, 1.3) | 0.885 |
| 30–34y | 1.0 (0.5, 1.4) | 0.354 | 0.9 (0.6, 1.2) | 0.960 | 2.1 (1.6, 2.7) | 0.741 | 1.3 (1.0, 1.5) | 0.618 |
| 35y | 0.4 (0.0, 1.0) | 0.864 | 1.1 (0.6, 1.7) | 0.539 | 2.3 1.2, 3.4 | 1.000 | 1.3 (0.9, 1.7) | 0.613 |
| ARI influenza by education level | ||||||||
| Junior high school (9th grade) or lower | 0.8 (0.3, 1.5) | REF | 0.9 (0.3, 1.6) | REF | 2.7 (1.7, 3.8) | REF | 1.5 (1.0, 2.0) | REF |
| Senior high school (12th) | 0.7 (0.3, 1.1) | 0.897 | 1.3 (0.9, 1.7) | 0.504 | 2.6 (1.9, 3.4) | 0.948 | 1.5 (1.2, 1.8) | 1.000 |
| College or higher | 0.7 (0.5, 0.9) | 0.732 | 1.0 (0.8, 1.1) | 1.000 | 1.9 (1.6, 2.3) | 0.181 | 1.1 (1.0, 1.2) | 0.100 |
| Syndrome | ||||||||
| ARI b | 0.7 (0.5, 0.9) | REF | 1.0 (0.8, 1.2) | REF | 2.1 (1.9, 2.4) | REF | 1.2 (1.1, 1.3) | REF |
| ILI c | 0.3 (0.2, 0.4) | <0.001 | 0.3 (0.2, 0.4) | <0.001 | 0.6 (0.4, 0.7) | <0.001 | 0.4 (0.3, 0.5) | <0.001 |
Abbreviations: CI, confidence interval; NA, not applicable; REF, reference.
The start of each influenza epidemic period was defined as the first day of three consecutive influenza reporting weeks in which the percentage of specimens testing positive for any influenza virus infection was higher than 5%. The end of each influenza epidemic period was defined as the day before the first of three consecutive influenza reporting weeks in which the percentage of specimens testing positive for influenza was below 5%.
ARI: acute respiratory illness, defined as ≥1 respiratory symptom (cough, sore throat, stuffy nose, chest pain, and difficulty breathing) and ≥1 systemic symptom (feverish, temperature ≥38°C, chills, headache); or ≥2 respiratory symptoms with onset within the last 10 days.
ILI: influenza‐like illness, defined as a measured temperature ≥38°C and cough/sore throat with onset within the last 10 days.