Factors associated with Acinetobacter baumannii lower respiratory tract infection in the respiratory intensive care unit patients: a cross-sectional observational study.

BACKGROUND: Immunosuppression is a crucial risk factor for susceptibility to and prognosis of Acinetobacter baumannii (A. baumannii) infection in patients in the respiratory intensive care unit (RICU). However, the role of the adaptive immune response as an associated factor for A. baumannii lower respiratory tract infection (LRTI) has not been fully elucidated. Therefore, this study aimed to examine the clinical value of adaptive immune response-related factors for A. baumannii LRTI in RICU patients. METHODS: A single-center retrospective cross-sectional observational study was conducted on 78 consecutive patients admitted to the RICU with an initial positive culture for A. baumannii, who were enrolled from Fuzhou Pulmonary (Thoracic) Hospital of Fujian Province between January 1 and December 31, 2023. According to the 2016 Clinical Practice Guidelines for the Management of Adults with Hospital-Acquired and Ventilator-Associated Pneumonia by the Infectious Diseases Society of America and the American Thoracic Society, and the Chinese Guidelines for the Diagnosis and Treatment of Adult Hospital-Acquired Pneumonia and Ventilator-Associated Pneumonia (2018 Edition) by the Chinese Medical Association, patients were divided into an infection group (n=51) and a colonization group (n=27). Demographic characteristics, underlying comorbidities, antimicrobial use prior to infection, peripheral blood cell counts, infection biomarkers including procalcitonin (PCT), C-reactive protein (CRP) and biochemical indicators including serum globulin (GLB) within 24 hours of symptom onset for patients in the A. baumannii LRTI group, or within 24 hours after collection of the first A. baumannii-positive culture specimen for those in the colonization group, as well as T lymphocyte subsets detected within 48 hours after admission to RICU were analyzed to examine the factors associated with A. baumannii LRTI. RESULTS: Peripheral blood lymphocytes counts, CD3+, CD4+, CD8+ lymphocyte counts as well as serum GLB level in the infection group were significantly lower than those in the colonization group (all P<0.05). The Sequential Organ Failure Assessment (SOFA) score, glucocorticoid use, the pre-infection use of carbapenems and β-lactamase inhibitor combinations were significantly higher in the infection group (all P<0.05). Multivariate binary logistic regression analysis identified serum GLB, pre-infection use of carbapenems and pre-infection use of β-lactamase inhibitor combinations as factors associated with A. baumannii LRTI in RICU patients (all P<0.05), with odds ratios (ORs) and 95% confidence interval (CI) of 0.830 (95% CI: 0.749-0.918), 8.823 (95% CI: 2.200-35.392), and 7.094 (95% CI: 1.834-27.446), respectively. The receiver operating characteristic (ROC) curve analysis showed area under the curve (AUC) values of 0.777 for GLB <27.45 g/L, 0.658 for pre-infection use of carbapenem, and 0.694 for pre-infection use of β-lactamase inhibitor combinations. The combined model (serum GLB combined with pre-infection use of carbapenems or β-lactamase inhibitor combinations) yielded an AUC of 0.805. CONCLUSIONS: Decreased serum GLB level may be a factor associated with A. baumannii LRTI in RICU patients, particularly among those with previous administration of broad-spectrum antibiotics.