Association between Air Pollutants and Initiation of Biological Therapy in Patients with Ankylosing Spondylitis: A Nationwide, Population-Based Case-Control Study

Abstract

Abstract Background: Outdoor air pollution has been found to trigger systemic inflammatory responses and aggravate the activity of certain rheumatic diseases. However, few studies have explored the influence of air pollution on the activity of ankylosing spondylitis (AS). As patients with active AS in Taiwan can be reimbursed through the National Health Insurance program for biological therapy, we investigated the association between air pollutants and the initiation of biologics for active disease in patients with AS. Methods: Since 2011, hourly concentrations of ambient air pollutants, including PM2.5, PM10, NO2, CO, SO2 and O3 have been estimated in Taiwan. Using Taiwanese National Health Insurance Research Database, we identified patients with newly diagnosed AS from 2003 to 2013. We selected 584 patients initiating biologics from 2012 to 2013 and 2,336 gender-, age at biologic initiation-, year of AS diagnosis- and disease duration-matched controls. We examined the associations of biologics initiation with air pollutants exposure within one year prior to biologic use while adjusting for potential confounders, including disease duration, urbanisation level, monthly income, Charlson comorbidity index (CCI), uveitis, psoriasis, inflammatory bowel disease and the use of medications for AS. Results are shown as adjusted odds ratio (aOR) with 95% confidence intervals (CIs). Results: The initiation of biologics was associated with exposure to CO (per 1 ppm) (aOR, 8.58; 95% CI, 2.02–36.35), and NO2 (per 10 ppb) (aOR, 0.23; 95% CI, 0.11–0.50). Other independent predictors included disease duration (incremental year, aOR, 8.97), CCI (aOR, 1.31), psoriasis (aOR, 25.06), use of non-steroidal anti-inflammatory drugs (aOR, 23.66), methotrexate use (aOR, 4.53; 95% CI, 2.93–7.00), sulfasalazine use (aOR, 12.15; 95% CI, 8.98–15.45) and prednisolone equivalent dosages (mg/day, aOR, 1.11). Conclusions: This nationwide, population-based study revealed that the initiation of biologics was positively associated with CO levels, but negatively associated with NO2 levels.