The application of mNGS of bronchoalveolar lavage fluid in dissecting pulmonary infections in patients with CTD-ILD

Abstract Objectives To evaluate the application of metagenomic next-generation sequencing (mNGS) of bronchoalveolar lavage fluid (BALF) in the diagnosis of pulmonary infection in patients with connective tissue disease-associated interstitial lung disease (CTD-ILD). Methods Patients with CTD-ILD who had been evaluated for suspected pulmonary infection by mNGS of BALF were identified, and were then categorized either as pulmonary infection or non-infectious disease progression of CTD-ILD based on clinical composite assessment. The performance of mNGS in the diagnosis of pulmonary infection was compared with that of conventional microbiological tests (CMTs). Results In the 48 patients with CTD-ILD who had been evaluated for pulmonary infection by mNGS of BALF, the majority (66.67%) were patients with idopathic inflammatory myopathy-associated ILD (IIM-ILD). According to the clinical composite assessment, 36 patients were classified as pulmonary infection and 12 as non-infectious disease progression. Cytomegalovirus (CMV), Pneumocystis jirovecii and aspergillus were among the most common causative pathogens. While mNGS was superior in identifying bacteria, viruses and P. jirovecii, CMTs identified more aspergillus and cryptococcus. Decreased albumin, reduced immunoglobulin M and increased lactate dehydrogenase (LDH) were predictors for pulmonary infections in CTD-ILD. Short disease duration, decreased lymphocytes and reduced immunoglobulins were predictive of infection with P. jirovecii. Older age and increased serum ferritin were more common in patients with aspergillus infection. Conclusion Pulmonary infections are common in patients with CTD-ILD. mNGS has the advantages of rapidly detecting more bacteria, viruses and P. jirovecii. However, infection with aspergillus should be more rigorously evaluated in combination with CMTs.