13% of surveyed workers reported respiratory symptoms with a higher prevalence in winter, particularly among welders. The adjusted OR in welders versus other manual labourers was 1.72 (95% CI 1.02 to 3.01) overall and 2.31 (1.05 to 5.10) in winter months; no effect was observed in summer. The risk of consultation for respiratory infections was higher in welders than in manual labourers, with an adjusted incidence rate ratio of 1.45 (1.59 to 1.83) overall, 1.47 (1.42 to 1.52) in winter and 1.33 (1.23 to 1