Association between air pollutants and RA disease activity
Regarding the association between PM2.5 and RA disease activity (DAS28 and SDAI), no statistically significant changes, in the week preceding the visit, were observed in the multivariable linear regression models (Table 2). PaGA, PhGA and TJC showed statistically significant association with PM2.5 only for some scattered days before the evaluation (Supplementary Table S5).
When therapy was studied, a significant interaction was found for PM2.5 at the day of the visit, resulting in an inverse association between PM2.5 and DAS28 for patients with b/tsDMARD and no significant association for patients untreated and treated with csDMARDs (Supplementary Figure S1).
Considering the association between PM10 and RA disease activity, a statistically significant change 5 days before the visit was observed (p=0.034) (Table 2). PhGA and TJC showed scattered statistically significant associations with PM10(Supplementary Table S6). The association between PM10and RA disease activity was not modified by therapy.
Association between NO2 and RA disease activity was significant at the day of the visit and at the day before (Table 3). PhGA showed a statistically significant association with NO2 the day before the visit and two days before (Supplementary Table S7). The association between NO2and RA disease activity was not modified by therapy.
O3 displayed an opposite trend, a statistically significant association was observed with DAS28, SDAI, GH and PhGA for exposures experienced the day preceding the visit, and five days before for DAS28 and PhGA. Interaction of O3 with therapy was particularly evident in several days before the visit (Table 3, Supplementary Table S8 and Figure S2).
Since there were no significant differences between the first and the second week before the evaluation, we reported only results referring to 7 days before the visit for all the pollutants considered.