Table 2.
Association Between Incidence of Pandemic Influenza A (H1N1-2009) and Climatic Factors at the County Level in Multilevel Poisson Regression,a People’s Republic of China, 2009
| Variable and Unitb | Daily Average Incidence | No. of Observations | Univariate Analysis |
Multivariate Analysis |
||||
| Crude % Change | 95% CI | P Value | Adjusted % Change | 95% CI | P Value | |||
| Temperature (categorical), °C | ||||||||
| <0 | 0.076 | 38,106 | ||||||
| 0–9 | 0.159 | 66,570 | ||||||
| 10–19 | 0.110 | 97,800 | ||||||
| 20–30 | 0.027 | 168,983 | ||||||
| >30 | 0.009 | 16,467 | ||||||
| Temperature (continuous), 10°C | 74.8 | 71.7, 77.9 | <0.001 | 76.3 | 73.2, 79.5 | <0.001 | ||
| Quadratic temperature (continuous), 100°C | −36.7 | −37.1, −36.3 | <0.001 | −34.9 | −35.3, −34.5 | <0.001 | ||
| Relative humidity (categorical), % | ||||||||
| <20 | 0.316 | 1,770 | ||||||
| 20–39 | 0.164 | 20,645 | ||||||
| 40–59 | 0.096 | 67,031 | ||||||
| 60–80 | 0.065 | 199,565 | ||||||
| >80 | 0.057 | 98,915 | ||||||
| Relative humidity (continuous), 10% | −4.4 | −4.8, −3.9 | <0.001 | −1.4 | −1.9, −0.9 | <0.001 | ||
| Precipitation (categorical), mm | ||||||||
| 0 | 0.088 | 208,047 | ||||||
| 0.01–1.00 | 0.063 | 167,906 | ||||||
| >1.00 | 0.022 | 11,973 | ||||||
| Precipitation (continuous), 1 mm | 1.0 | 1.0, 1.0 | 0.184 | NS (excluded) | ||||
| School summer vacation and public holidays | ||||||||
| No | 0.113 | 187,797 | 1.0 | 1.0 | ||||
| Yes | 0.039 | 200,129 | −62.3 | −62.8, −61.8 | <0.001 | −36.4 | −37.2, −35.5 | <0.001 |
| Proportion of school-age population (categorical), % | ||||||||
| <18 | 0.094 | 121,412 | ||||||
| 18–22 | 0.062 | 132,302 | ||||||
| >22 | 0.070 | 134,212 | ||||||
| Proportion of school-age population (continuous), 10% | −19.7 | −28.9, −9.4 | <0.001 | NS (excluded) | ||||
| Population density (categorical), per km2 | ||||||||
| <120 | 0.083 | 92,787 | ||||||
| 120–299 | 0.039 | 95,396 | ||||||
| 300–700 | 0.043 | 96,416 | ||||||
| >700 | 0.130 | 103,327 | ||||||
| Population density (continuous), 1,000 persons per km2 | 13.1 | 10.2, 16.1 | <0.001 | 14.8 | 11.8, 18.0 | <0.001 | ||
| Density of medical facilities (categorical), per 10,000 people | ||||||||
| <0.8 | 0.028 | 146,343 | ||||||
| 0.8–1.1 | 0.052 | 71,734 | ||||||
| >1.1 | 0.125 | 169,849 | ||||||
| Density of medical facilities (continuous), per 10,000 people | 62.5 | 52.3, 73.3 | <0.001 | 43.5 | 35.3, 52.3 | <0.001 | ||
Abbreviations: CI, confidence interval; NS, not significant.
a
Results were adjusted for school summer vacation and public holidays, population density, and the density of medical facilities.
b
For all continuous variables, categorical results are also reported to allow inspection of the data and assessment of whether or not the assumption regarding continuous variables was justified.