Risk of a PEF episode starting within seven days of an upper respiratory tract infection according to personal exposure to NO2
| NO2 exposure level (μg/m3) | No of upper respiratory episodes | No of PEF episodes | RR | 95% CI |
|---|---|---|---|---|
| ⩽8 | 95 | 21 | 1 | |
| 8–13 | 83 | 19 | 1.1 | 0.6 to 1.8 |
| 13–28 | 69 | 19 | 1.2 | 0.7 to 2.1 |
| >28 | 26 | 11 | 1.9 | 1.1 to 3.4 |
Exposures to NO2 were estimated for the seven day period starting two days before the onset of the relevant upper respiratory episode by a method described in the text.
p for trend = 0.04.