Table 1

Study population characteristics for 50 new recruit firefighters at baseline and follow-up

n (%)Mean (SD)
Male49 (98)
Female1 (2)
Hispanic6 (12)
Non-Hispanic44 (88)
White47 (94)
Black3 (6)
BMI (kg/m2) at baseline26.0 (2.9)
Baseline visitFollow-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-hours26.4 (0.4)
Fire-runs48.4 (0.4)
Days since most recent fire17.7 (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 (%)†
Neutrophils0.55 (0.24)0.58 (0.10)
CD4+ T cells0.12 (0.07)0.13 (0.05)
CD8+ T cells0.11 (0.06)0.11 (0.04)
Monocytes0.11 (0.08)‡0.08 (0.03)‡
B cells0.06 (0.03)0.06 (0.02)
Natural killer cells0.06 (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.