Study population characteristics for 50 new recruit firefighters at baseline and follow-up
| n (%) | Mean (SD) | |
| Male | 49 (98) | |
| Female | 1 (2) | |
| Ethnicity | ||
| Hispanic | 6 (12) | |
| Non-Hispanic | 44 (88) | |
| Race | ||
| White | 47 (94) | |
| Black | 3 (6) | |
| BMI (kg/m2) at baseline | 26.0 (2.9) | |
| Baseline visit | Follow-up visit | |
| Mean (SD) | Mean (SD) | |
| Age (years) | 28.0 (5.9) | 30.2 (6.0) |
| Time in between visits (months) | – | 26.5 (4.5) |
| Fire exposure between baseline and follow-up* | ||
| Fire-hours | – | 26.4 (0.4) |
| Fire-runs | – | 48.4 (0.4) |
| Days since most recent fire | 17.7 (1.8) | |
| Fire-hours (structure only) | -- | 13.2 (0.5) |
| Fire-runs (structure only) | -- | 16.3 (0.5) |
| Days since most recent fire (structure only) | 28.9 (2.4) | |
| Estimated cell type proportions (%)† | ||
| Neutrophils | 0.55 (0.24) | 0.58 (0.10) |
| CD4+ T cells | 0.12 (0.07) | 0.13 (0.05) |
| CD8+ T cells | 0.11 (0.06) | 0.11 (0.04) |
| Monocytes | 0.11 (0.08)‡ | 0.08 (0.03)‡ |
| B cells | 0.06 (0.03) | 0.06 (0.02) |
| Natural killer cells | 0.06 (0.03) | 0.06 (0.03) |
| Estimated smoking§ | ||
| Pack years | −20.4 (7.1) | 0.8 (6.9) |
| Pack years residual | −21.7 (7.6) | −0.5 (7.3) |
*For the fire exposure variables, fire-hours indicates cumulative time at fires since follow-up; fire-runs indicates the cumulative number of fire-runs since follow-up; These are listed for all fire incident types as well as for structural-only. Geometric means and SD are listed as the distributions were skewed.
†Cell type proportions are estimated from DNA methylation data according to the established algorithm by Houseman et al. 39
‡Differed across time points (p<0.05 for paired t-test for unequal variances).
§Lifetime smoking pack-years were estimated from the DNA methylation data using an algorithm by Lu et al.40 All participants reported being non-smokers at time of the study, but this algorithm also estimates past exposure to smoking; values are relative and not absolute.
BMI, body mass index.