The effect of air pollution exposure on risk of outpatient visits for Sjogren's syndrome: A time-series study

Abstract

Background: Emerging evidence showed that air pollutants are associated with development and recurrence of autoimmune disorders, but there is scarce evidence regarding the relationship between air pollutants and Sjogren's syndrome (SS). We sought to investigate whether air pollutants affect the risk of outpatient visits for SS and to quantify the burden of SS visits attributable to air pollution exposure in Hefei, China.

Methods: Daily data on outpatient visits for SS, air pollutants and meteorological data in Hefei, China, from January 1, 2015 to December 31, 2020 were obtained. A distributed lag non-linear model in conjunction with a generalized linear model were employed to assess the relationship between air pollution and SS outpatient visits. Stratified analyses were further performed by gender, age and season. Attributable fraction (AF) and attributable number (AN) were used to reflect disease burden.

Results: There were 4501 records of outpatient visits for SS. Exposure to PM_2.5 was associated with increased risk of SS outpatient visits (relative risk (RR) = 1.218, 95% confidence interval (CI): 1.017-1.458, lag 0-14 day). An increase of 24 μg/m³ (interquartile range) in NO₂ concentration was associated with 26.3% increase in the risk of SS outpatient visits (RR = 1.263, 95%CI: 1.105-1.445, lag 0-10 day). In contrast, exposure to O₃ was associated with decreased risk of SS outpatient visits (RR = 0.692, 95%CI: 0.510-0.939, per 63 μg/m³ in O₃ exposure, lag 0-27 day). Stratified analyses showed that females (vs. males) was more vulnerable to SS outpatient visits associated with NO₂ and O₃ exposure. SS patients aged ≥65 years (vs. aged <65 years) were susceptible to PM_2.5 exposure. Exposure to PM_2.5 or NO₂ in the cold season was associated with higher risk of SS outpatient visits than that in the warm season. In addition, the AN (232, 95%CI: 119, 324) and AF (5.16%, 95%CI: 2.55%, 7.21%) of NO₂ exposure were higher than those of PM_2.5 exposure.

Conclusion: PM_2.5 and NO₂ exposure are associated with increased risk of SS outpatient visits, while O₃ exposure appears to be associated with decreased risk of SS outpatient visits. The effect of air pollutants exposure on risk of SS outpatients can be modified by age, gender and season. The burden of SS outpatient visits attributable to NO₂ exposure is higher than those attributable to PM_2.5 exposure.

Keywords: Air pollution; Outpatient visits; Sjogren's syndrome; Time-series analysis.