Table 1

Description of changes in input parameters in the dynamic population model to evaluate the impact of different intervention scenarios

Intervention scenarioDescription of parameter changeChange in model input parameters
Flour dust exposureFungal α-amylasePopulation parameters*
No interventionGM=1.19
GSDbw=2.29
GSDww=2.27
GM=0.57
GSDbw=2.77
GSDww=4.57
Prob_atopy=0.3
Covenant intervention▸For first 6 years, population GM exposure decreases by 2% annually for flour dust and 8% annually for fungal α-amylase
▸After the 6-year level, exposures stay constant
▸Variability is assumed to stay the same
Year t=1–6; GM=GM(t−1)×0.98
Year t=7–20; GM=1.05
GSDbw=2.29
GSDww=2.27
Year t=1–6; GM=GM(t−1)×0.92
Year t=7–20; GM=0.35
GSDbw=2.77
GSDww=4.57
Prob_atopy=0.3
Continuation of covenant▸Equal to the above described scenario
▸However, the decrease in the GM values for both exposures is continued for the full 20-year period
GM=GM(t−1)×0.98
GSDbw=2.29
GSDww=2.27
GM=GM(t−1)×0.92
GSDbw=2.77
GSDww=4.57
Prob_atopy=0.3
Hygiene intervention▸Individual exposure estimates from the baseline measurement dataset are recalculated according to the reduction factors derived previouslyGM=0.82
GSDbw=2.03
GSDww=2.05
GM=0.39
GSDbw=2.56
GSDww=4.44
Prob_atopy=0.3
Health surveillance intervention (I)αExposures of high risk individuals (sensitised workers) are reduced by 90%
▸Individual workers can only receive an intervention once
▸The population variability of exposure is assumed to remain unchanged
High risk individuals:
GMpost-int=0.1×GMpre-int
Others:
GMpost-int=GMpre-int
GSDbw=2.29
GSDww=2.27
High risk individuals:
GMpost-int=0.1×GMpre-int
Others:
GMpost-int=GMpre-int
GSDbw=2.77
GSDww=4.57
Prob_atopy=0.3
Health surveillance intervention (II)▸As above, but now non-sensitised workers with rhinitis symptoms are also included in the definition of high risk workersHigh risk individuals:
GMpost-int=0.1×GMpre-int
Others:
GMpost-int=GMpre-int
GSDbw=2.29
GSDww=2.27
High risk individuals:
GMpost-int=0.1×GMpre-int
Others:
GMpost-int=GMpre-int
GSDbw=2.77
GSDww=4.57
Prob_atopy=0.3
Pre-employment screening▸Exposure parameters are not affected
▸The probability of atopy for new employees is set to 0 assuming no atopic subjects enter the workforce
GM=1.19
GSDbw=2.29
GSDww=2.27
GM=0.57
GSDbw=2.77
GSDww=4.57
Prob_atopy=0
  • * Only the probability of being atopic (Prob_atopy) is relevant for the evaluated intervention strategies.

  • GM, geometric mean exposure level; GMpre-int, individual exposure estimate before receiving an individual intervention; GMpost-int, individual exposure estimate after receiving an individual intervention; GSDbw, the between worker or inter-individual exposure variability; GSDww, the day-to-day or intra-individual exposure variability.