Table 2.
Risk analysis of covariates associated with reported cases of influenza.
| Covariates | Crude OR (95% CI)* | Adjusted OR (95% CI)** | Adjusted OR (95% CI)† |
|---|---|---|---|
| Flu vaccines (per million doses)‡ | 0.528(0.527~0.529) | 0.645(0.644~0.647) | 0.873(0.825~0.923) |
| Flu surveillance protocols# | |||
| Version 1 (2005–2008) | 1 [Reference] | 1 [Reference] | 1 [Reference] |
| Version 2 (2009–2016) | 3.366(3.349~3.383) | 4.614(4.588~4.640) | 1.045(0.819~1.331) |
| Version 3 (2017–2018) | 11.79(11.73~11.85) | 8.381(8.332~8.431) | 1.656(1.097~2.496) |
| Rate of influenza A (H1N1)pdm09¶ | 1.149(1.148~1.151) | 1.117(1.114~1.120) | 1.195(1.005~1.413) |
| Percentage of influenza A (H1N1)pdm09†† | 1.206(1.205~1.207) | 0.969(0.968~0.970) | 1.015(0.958~1.076) |
| Population density (/km2) | 18.29(18.13~18.46) | 5.597(5.546~5.649) | 2.475(0.642~9.543) |
| Latitude (degree) | 0.940(0.940~0.940) | 0.953(0.952~0.953) | 0.985(0.980~0.991) |
| Longitude (degree) | 0.998(0.997~0.998) | 0.998(0.998~0.998) | 0.998(0.997~0.999) |
Abbreviations: OR, odds ratio; CI, confidence interval.
*Univariate Poisson analysis models.
**Multivariate adjusted Poisson analysis model, which included all variables in the univariate analysis models.
†Multivariate adjusted spatiotemporal models, which included all variables in the univariate analysis models; an intercept (α); a spatially unstructured random effect term (νi); a spatially structured conditional autoregression term (υi); a first-order random walk-correlated time variable (γ1j); and an interaction term for time and place (δij).
‡Total number of flu vaccines approved for sale by China’s National Institute for Food and Drug Control (NIFDC), which were rescaled to one million doses as one unit. Data were collected from NIFDC.
#The influenza surveillance protocols used included three versions: Version 1 for 2005 to 2008, Version 2 for 2009 to 2016, and Version 3 for 2017 to 2018.
¶The rate of influenza A (H1N1)pdm09 was calculated by dividing the number of specimens of positive influenza A (H1N1)pdm09 viruses by the number of specimens processed from the influenza likely illness (ILI) cases. The rate was rescaled to 10% changes as one unit. Data were collected from FluNet (www.who.int/flunet), Global Influenza Surveillance and Response System (GISRS).
†††The percentage of influenza A (H1N1)pdm09 was calculated by dividing the number of specimens of positive influenza A (H1N1)pdm09 viruses by the total number of specimens of influenza-positive viruses. One unit change equals a 10% change in influenza A (H1N1)pdm09.