Table 2.
Univariate Analyses on Factors Associated With the Detection of Influenza Viral RNA in Air
| Variable | Analyzed Events, No. | Positive Events, No. (%) | Unadjusted OR (95% CI) | P Value |
|---|---|---|---|---|
| Sampling date | ||||
| Holiday | 184 | 17 (9.2) | Reference | Reference |
| Teaching date | 510 | 126 (24.7) | 3.22 (1.93–5.70) | < .001 |
| Sampling location | ||||
| Canteen | 296 | 66 (22.3) | Reference | Reference |
| Lecture hall | 122 | 27 (22.1) | 0.99 (.59–1.63) | .970 |
| Shuttle bus | 136 | 21 (15.4) | 0.64 (.36–1.08) | .101 |
| UHS | 140 | 29 (20.7) | 0.91 (.55–1.48) | .709 |
| Crowdedness (No. of occupants on site)a | ||||
| Low | 215 | 31 (14.4) | Reference | Reference |
| Intermediate | 229 | 40 (17.5) | 1.26 (.76–2.11) | .382 |
| High | 250 | 72 (28.8) | 2.40 (1.51–3.88) | < .001 |
| Ventilation rate (L/sec/person)b | ||||
| Low | 233 | 55 (23.6) | Reference | Reference |
| Intermediate | 222 | 50 (22.5) | 0.94 (.61–1.46) | .784 |
| High | 239 | 38 (15.9) | 0.61 (.38–.97) | .036 |
| Indoor CO2 level (ppm)c | ||||
| Low | 228 | 40 (17.5) | Reference | Reference |
| Intermediate | 220 | 39 (17.7) | 1.01 (.62–1.65) | .959 |
| High | 246 | 64 (26.0) | 1.65 (1.06–2.59) | .027 |
| Indoor temperature (°C) | ||||
| Numeric | 694 | 143 (20.6) | 1.15 (1.06–1.24) | < .001 |
| Indoor RH (%) | ||||
| Numeric | 694 | 143 (20.6) | 1.00 (.98–1.02) | .752 |
| Indoor AH (kg/m3) | ||||
| Numeric (per 0.002 increase) | 694 | 143 (20.6) | 1.1 (.99–1.27) | .083 |
| Temperature difference (indoor-outdoor) (°C) | ||||
| Numeric | 694 | 143 (20.6) | 0.92 (.87–.98) | .006 |
| RH difference (indoor-outdoor) (%) | ||||
| Numeric | 694 | 143 (20.6) | 1.00 (.99–1.01) | .895 |
| AH difference (indoor-outdoor) (kg/m3) | ||||
| Numeric (per 0.002 increase) | 694 | 143 (20.6) | 0.89 (.81–.97) | .012 |
| Flu activity: influenza detection rate (%) | ||||
| Numeric | 694 | 143 (20.6) | 0.97 (.94–1.00) | .033 |
Abbreviations: AH, absolute humidity; CI, confidence interval; CO2, carbon dioxide; OR, odds ratio; RH, relative humidity; UHS, University Health Service.
aNumber of occupants was categorized into high, intermediate, and low based on the numeric data distribution: high (upper 33% percentile), intermediate (middle 33% percentile), and low (lower 33% percentile).
bVentilation was categorized into high, intermediate, and low based on the numeric data distribution: high (upper 33%), intermediate (middle 33%), and low (lower 33%).
cIndoor CO2 concentration was categorized into high, intermediate, and low based on the numeric data distribution: high (upper 33% percentile), intermediate (middle 33% percentile), and low (lower 33% percentile).