Abstract: Objective To investigate the risk factors of secondary pulmonary infection (PI) in the elderly patients with idiopathic interstitial pneumonia (IIP), and to establish a predictive model. Methods A total of 248 patients with IIP treated in Dazhou Dachuan District People’s Hospital from January 2020 to January 2024 were selected and divided into IIP group and IIP-PI group according to whether they presented with secondary PI during hospitalization. The influencing factors of secondary PI in IIP patients were analyzed by multiple Logistic regression, and the prediction model was constructed. Receiver operating characteristic (ROC) curve was used to analyze the predictive value of the prediction model for secondary PI in the elderly patients with IIP. Results Among 248 patients with IIP, 75 cases (30.24%) presented with PI. The age, disease course, the levels of white blood cell count and C-reactive protein (CRP), and the proportion of combined diabetes mellitus, prophylactic antibiotics and daily hormone use ≥30 mg in IIP-PI group were higher than those in IIP group, and the level of albumin was lower than that in IIP group (P<0.05). Multivariate Logistic regression analysis showed that age, combined diabetes, prophylactic use of antibiotics, course of disease, daily dose of hormone, white blood cell count and CRP were independent risk factors for secondary PI, and albumin was an independent protective factor (P<0.05). The AUC of Logistic regression model for predicting PI secondary to IIP was 0.929 (95%CI: 0.889－0.958). Conclusions Age, combined diabetes, prophylactic antibiotic use, course of disease, daily hormone use, white blood cell count, CRP and albumin are the influential factors for secondary PI in the elderly patients with IIP. The risk prediction model based on the above factors can be used as an important tool for secondary PI.

Key words: idiopathic interstitial pneumonia, lung infection, risk factor, prediction model