Table 4

Incident RA in relation to regular field work and tasks at enrolment, overall and in applicators only

Overall*Applicators only†
RA cases
n=351
RA cases
n=120
N (%)HR (95% CI)‡P valueN (%)HR (95% CI)‡P value
Field work
 Till soil (cultivate, disc, plough)163 (47)1.02 (0.75 to 1.37)0.92111 (95)1.32 (0.57 to 3.05)0.52
 Plant183 (53)1.23 (0.83 to 1.62)0.14110 (94)1.31 (0.61 to 2.35)0.49
 Use natural fertiliser (manure)105 (31)1.04 (0.78 to 1.37)0.7970 (61)1.09 (0.72 to 1.63)0.69
 Use chemical fertiliser145 (42)1.50 (1.11 to 2.02)0.009100 (85)1.25 (0.66 to 1.88)0.41
 Drive combines
  ≤62 years116 (34)1.03 (0.73 to 1.45)0.8647 (73)0.59 (0.31 to 1.17)0.13
  >62 years43 (84)2.46 (1.05 to 5.78)0.039
 Handpick crops114 (33)1.17 (0.92 to 1.50)0.2146 (40)1.21 (0.79 to 1.89)0.37
Other tasks and exposures
 Milk cows
  ≤62 years6 (2)0.59 (0.26 to 1.33)0.202 (2)NA
  >62 years6 (2)1.83 (0.80 to 4.21)0.155 (4)2.56 (1.01 to 6.53)0.049
 Vet procedures
  ≤62 years66 (19)0.92 (0.68 to 1.25)0.6122 (18)0.71 (0.40 to 1.25)0.23
  >62  years20 (17)1.51 (0.82 to 2.79)0.19
 Grind feed
  ≤62 years63 (19)1.14 (0.82 to 1.59)0.4326 (22)1.00 (0.56 to 1.78)0.43
  >62 years23 (19)1.90 (0.99 to 3.62)0.053
  Drive trucks158 (50)0.94 (0.74 to 1.19)0.5975 (36)0.86 (0.64 to 1.15)0.30
 Diesel tractor
  ≤62 years106 (31)0.78 (0.55 to 1.11)0.1783 (72)1.02 (0.67 to 1.58)0.91
  >62 years71 (20)1.26 (0.78 to 2.04)0.35
 Gasoline tractor135 (44)0.91 (0.70 to 1.17)0.4475 (64)0.78 (0.53 to 1.16)0.22
 Welding83 (25)1.15 (0.78 to 1.69)0.4780 (63)1.38 (0.90 to 2.11)0.13
 Repairing engines59 (18)1.19 (0.84 to 1.69)0.3256 (48)1.29 (0.89 to 1.88)0.18
 Grind metal87 (26)1.11 (0.75 to 1.64)0.6281 (70)1.12 (0.73 to 1.70)0.61
 Use gasoline to clean83 (25)1.06 (0.80 to 1.39)0.7047 (40)1.03 (0.70 to 1.51)0.89
 Use other solvents to clean91 (27)1.40 (1.09 to 1.80)0.00934 (29)1.26 (0.84 to 1.89)0.26
 Painting§132 (39)1.26 (1.00 to 1.59)0.04846 (39)0.98 (0.67 to 1.43)0.98
  • *Results shown for combined sample of applicators who completed the ‘take home’ questionnaire (120 cases and 13 436 non-cases) and enrolled spouses (231 cases and 20 842 non-cases).

  • †Data from the applicator ‘take-home’ questionnaire only.

  • ‡Hazard model adjusted for state, participant type (applicator/spouse), smoking pack-years, education and pesticides; NA for less than five exposed cases. HRs allowed to vary by the median age (ie, 62 years) when proportional hazards assumption was not met (p≤0.10).

  • §Interaction by sex, p=0.055, HR=1.42 in spouses (95% CI 1.07 to 1.89).

  • NA, not applicable; RA, rheumatoid arthritis.