Table 6

 Directly measured SHS exposure and the prospective risk of admission to hospital for asthma

Exposure/dose measurementRisk of hospital admission HR* (95% CI)Baseline risk of hospital admission (time-dependent model)†HR (95% CI)
*Multivariate Cox proportional hazards regression analysis controlling for age, sex, race, educational attainment, marital status, and previous smoking history. The overall rate of readmission to hospital was 40% for the nicotine badge group and 38% for the hair groups.
†Proportional hazards assumption was violated for this model (interaction between hair nicotine during the previous month and time, p = 0.08). The hazards ratio (HR) represents the risk of hospital admission at the baseline of the prospective follow up period; the risk diminished thereafter (see text). The proportional hazards assumption was not violated for the other models so time-dependent analyses are not presented.
NA  =  model not applicable (as described above).
Nicotine badge (previous week)
    First tertile (0–0.03 μg/m3)1.0 (referent)NA
    Second tertile (0.04–0.13 μg/m3)0.70 (0.39 to 1.26)NA
    Third tertile (0.14–9.82 μg/m3)0.94 (0.53 to 1.65)NA
Hair nicotine (previous month†)
    First tertile (0 ng/mg)NA1.0 (referent)
    Second tertile (0.01–0.12 ng/mg)NA3.73 (1.04 to 13.3)
    Third tertile (0.13–3.15 ng/mg)NA3.61 (1.01 to 12.9)
Hair nicotine (previous 2–3 months†)
    First tertile (0–0.02 ng/mg)1.0 (referent)NA
    Second tertile (0.03–0.19 ng/mg)0.61 (0.28 to 1.31)NA
    Third tertile (0.20–4.0 ng/mg)0.88 (0.43 to 1.79)NA
Hair cotinine (previous month†)
    First tertile (0–0.02 ng/mg)1.0 (referent)NA
    Second tertile (0.03–0.10 ng/ml)1.15 (0.57 to 2.33)NA
    Third tertile (0.11–0.78 ng/ml)1.40 (0.68 to 2.87)NA
Hair cotinine (previous 2–3 months†)
    First tertile (0–0.03 ng/ml)1.0 (referent)NA
    Second tertile (0.04–0.10 ng/ml)2.08 (0.96 to 4.54)NA
    Third tertile (0.11–1.11 ng/ml)1.80 (0.81 to 4.00)NA