Adjusted analysis of air quality measures by number of active waterpipes, August–September 2012, Toronto Waterpipe Study
| Air quality measures | Model | Waterpipe level | Adjusted coefficient (95% CI) | Exponential coefficient* | p Value |
|---|---|---|---|---|---|
| PM2.5 (µg/m3) | 1† | Background | Referent | ||
| 0 active waterpipe | 0.19 (−0.18 to 0.55) | 1.21 | 0.552 | ||
| 1–4 active waterpipes | 0.67 (0.36 to 0.97) | 1.95 | <0.001 | ||
| 5–9 active waterpipes | 0.90 (0.68 to 1.12) | 2.46 | <0.001 | ||
| 10+ active waterpipes | 1.25 (1.01 to 1.49) | 3.49 | <0.001 | ||
| 2‡ | Linear trend | 0.30 (0.10 to 0.49) | 1.35 | 0.003 | |
| Ambient CO (ppm) | 1† | Background | Referent | ||
| 0 active waterpipe | 0.15 (−0.07 to 0.37) | 1.16 | 0.192 | ||
| 1–4 active waterpipes | 0.62 (0.44 to 0.80) | 1.86 | <0.001 | ||
| 5–9 active waterpipes | 1.21 (1.06 to 1.35) | 3.35 | <0.001 | ||
| 10+ active waterpipes | 1.28 (1.12 to 1.45) | 3.60 | <0.001 | ||
| 2‡ | Linear trend | 0.09 (−0.01 to 0.18) | 1.09 | 0.066 | |
| Nicotine (µg/m3) | 1† | 1–4 active waterpipes | Referent | ||
| 5–9 active waterpipes | 5.35 (−3.35 to 14.06) | – | 0.175 | ||
| 10+ active waterpipes | 4.73 (−0.24 to 9.70) | – | 0.058 | ||
| 2‡ | Linear trend | 1.97 (−0.32 to 4.27) | – | 0.070 |
*Real-time measures of PM2.5 and ambient CO were log transformed in adjusted analysis and exponentiated to normal scale.
†In model 1, the number of active waterpipes was treated as a categorical variable. Mixed-model analysis was used for real-time measures of PM2.5 and ambient CO, compared with background measures and adjusted for temperature, relative humidity and CO2. Ordinary linear regression was used for measures of nicotine, compared with the level with 1–4 active waterpipe and adjusted for temperature, relative humidity, CO2, venue volume and distance from the nearest active waterpipe to the monitor.
‡In model 2, the number of active waterpipes was treated as a continuous variable (ie, 1, 2, 3 and 4 for levels with 0, 1–4, 5–9 and 10+ active waterpipes for PM2.5 and ambient CO in mixed model analysis; and 1, 2 and 3 for levels with 1–4, 5–9 and 10+ active waterpipes for nicotine measures in ordinary linear regression analysis). Analysis in model 2 was adjusted for temperature, relative humidity, CO2, venue volumes, door or window openings and distance from the nearest active waterpipe to monitors.
CO, carbon monoxide.