Conditional logistic multivariable regression models of influenza A or influenza B matched for gender, age and geographical region, and adjusted for education, country of birth, COPD, IHD, diabetes and use of corticosteroids in relation to the different dimensions of transmission and mitigation factors (model 2) in a national case–control study covering 1 July 2006 to 31 December 2019
| Dimensions of transmission and mitigation factors | Influenza A and influenza B | |
| ORs with 95% CI | ||
| Influenza A (N=11 300) | Influenza B (N=3671) | |
| No of workers in close proximity to each other* | ||
| <10 per day | 1.05 (0.99 to 1.12) | 0.98 (0.88 to 1.10) |
| 10–30 per day | 1.14 (1.07 to 1.22) | 1.17 (1.04 to 1.32) |
| >30 per day | 1.28 (1.20 to 1.37) | 1.22 (1.09 to 1.36) |
| Nature of contacts* | ||
| In workspaces with coworkers only | 1.05 (0.99 to 1.12) | 1.01 (0.90 to 1.12) |
| In workspaces with general public | 1.12 (1.05 to 1.20) | 1.09 (0.97 to 1.21) |
| Regular contacts with infected patients | 1.41 (1.31 to 1.51) | 1.37 (1.21 to 1.56) |
| Contaminated workspaces* | ||
| Frequently sharing material/surfaces with coworkers (≥10 times/day) | 1.08 (1.01 to 1.15) | 1.03 (0.92 to 1.15) |
| Sometimes sharing material/surfaces with general public (<10 times/day) | 1.06 (0.94 to 1.19) | 1.06 (0.86 to 1.30) |
| Frequently sharing materials/surfaces with general public (≥10 times/day) | 1.23 (1.16 to 1.31) | 1.19 (1.07 to 1.32) |
| Location* | ||
| Mostly working outside | 1.26 (1.02 to 1.55) | 1.16 (0.79 to 1.69) |
| Working partly inside | 1.09 (0.98 to 1.21) | 1.10 (0.91 to 1.32) |
| Working mostly inside | 1.16 (1.10 to 1.22) | 1.11 (1.01 to 1.22) |
| Social distancing* | ||
| Always maintained | 1.05 (0.97 to 1.14) | 1.05 (0.98 to 1.14) |
| Not always maintained | 1.07 (0.98 to 1.16) | 1.15 (1.06 to 1.25) |
| Never maintained | 1.40 (1.27 to 1.55) | 1.26 (1.18 to 1.36) |
| Physical proximity | ||
| 3rd vs 2nd and 1st | 1.11 (1.05 to 1.18) | 0.99 (0.89 to 1.09) |
| 4th vs 2nd and 1st | 1.39 (1.30 to 1.49) | 1.26 (1.12 to 1.41) |
| Exposure to diseases or infections | ||
| 2nd vs 1st | 1.13 (1.06 to 1.20) | 1.19 (1.08 to 1.32) |
| 3rd vs 1st | 1.17 (1.09 to 1.25) | 1.17 (1.04 to 1.31) |
| 4th vs 1st | 1.51 (1.40 to 1.63) | 1.42 (1.23 to 1.65) |
*Compared with homeworkers or working alone.
COPD, chronic obstructive pulmonary disease; IHD, ischaemic heart disease.