Respiratory infection risk in primary Sj?gren's syndrome complicated with interstitial lung disease: a retrospective study

Objectives To explore clinical and laboratory characteristics of primary Sjogren's syndrome (pSS) complicated with interstitial lung disease (ILD) and investigate the risk factors for respiratory infections in pSS-ILD.Methods A cohort of 162 pSS-ILD patients in Peking University People's Hospital from 2015 to 2020 were included, and all medical records were completely collected. We screened 53 patients suffering from respiratory infections as study cases, compared with 109 age- and sex-matched controls. Differences between infection group and control group were compared. Univariate and multivariate binary logistic regression tests were conducted to identify potential risk factors for respiratory infections in pSS-ILD patients.Results Among 162 pSS-ILD patients, 32.72% (53/162) suffered from respiratory infections. The most frequent type of ILD was nonspecific interstitial pneumonia (32.08%, 51/159), and the most common type of pathogen was bacteria (64.25%, 34/53). Infection group showed higher levels of ESSDAI (P < 0.001), CRP (P < 0.001), ESR (P = 0.003), and C3 (P = 0.020) but lower level of DLCO-(SB) (P = 0.015). Univariate logistic model revealed that PAH and the use of glucocorticoid increased infection risk in pSS-ILD patients. On multivariate logistic regression analysis, PAH (OR = 3.993, 95% CI = 1.192-13.373, P = 0.025) and severe reduction of DLCO (DLCO-(SB) < 40%, OR = 4.625, 95% CI = 1.281-16.702, P = 0.019) were significantly associated with increased risk of respiratory infections in pSS-ILD patients.Conclusion Among pSS-ILD patients, the most frequent type of ILD was nonspecific interstitial pneumonia. In patients with infection, bacteria were the most common pathogen. Higher levels of ESSDAI, CRP, ESR, and C3 may be correlated with increased infection risk. PAH and reduction of DLCO were identified as independent risk factors.