Risk Factors and Prediction Model for Positive Bacterial Culture in Lower Respiratory Tract during Stable Phase in Bronchiectasis

Background: Bronchiectasis is defined as a chronic inflammatory airway disease, which is characterized by abnormal, permanent dilation of the bronchi. Bacterial infection and colonization are regarded as a key etiological factor in its pathogenesis and a common cause of clinical exacerbations. Sputum culture remains a conventional diagnostic method. Because it’s not routinely performed in clinical practice for patients during the stable phase of bronchiectasis, those with bacterial colonization in the stable phase are often overlooked. Methods: The prospective study included 380 patients during the stable phase of bronchiectasis, who were enrolled from Longhua Hospital Affiliated to Shanghai University of Traditional Chinese Medicine between January 2020 and December 2024. Based on the result of sputum culture, the cohort was stratified into two groups: the culture-positive group (n = 208) and the culture-negative group (n = 172). Data analysis was performed using SPSS 27.0 and R 4.4.2. Univariate logistic analyses, LASSO regression and multivariate logistic analyses identified variables significantly associated with positive bacterial culture in lower respiratory tract. Developing a nomogram model of the risk factor based on the result of multivariate analysis, and evaluating clinical utility of the risk prediction model. Results: A total of 380 patients in the stable phase of bronchiectasis were enrolled, among whom positive detection rate for bacteria culture was 54.74%. And the bacteria detected by sputum culture, in descending order of prevalence, were Pseudomonas aeruginosa (65.87%), Haemophilus influenzae (13.46%), Streptococcus pneumoniae (6.25%), Moraxella catarrhalis (5.29%), Staphylococcus aureus (3.37%), Acinetobacter baumannii (2.88%), and Klebsiella pneumoniae (2.88%). A nomogram model was developed using multivariate analysis results, including 8 items: history of smoking, number of lobes affected ≥ 3, number of annul exacerbation ≥ 3, P.aeruginosa colonization within 1 year, other bacterial colonization within 1 year, history of hemoptysis within 1 year, CRP, CD3 + CD4 + T-cell count<500 cells/µL. The area under the curve (AUC) was 0.866 (95%CI: 0.831–0.902), indicating excellent discriminatory capacity. The Hosmer-Lemeshow goodness-of-fit test indicated strong calibration ( P  = 0.986). The DCA curve indicated robust clinical applicability of the model. Conclusion: The nomogram model demonstrated satisfactory discrimination and calibration accuracy. The model could help raise clinical awareness of the necessity of including sputum culture as a routine test for the patients during the stable phase of bronchiectasis, screen populations at high risk of chronic bacterial colonization, facilitate the timely initiation of antibiotics, prevent acute exacerbations, and control disease progression.