Nocardia spp. isolation in chronic lung diseases: pulmonary nocardiosis versus colonization - a comparative analysis

<bold>Introduction:</bold> <italic>Nocardia</italic> spp. are not typically found in human flora. Its detection in respiratory samples does not necessarily imply disease but individuals with chronic lung diseases (CLD) have a higher risk. <bold>Objectives:</bold> Characterize <italic>Nocardia</italic> spp. isolation in patients with CLD, assess its clinical and functional impact and discern differences between pulmonary nocardiosis (PN) and <italic>Nocardia</italic> spp. colonization (NC). <bold>Methods:</bold> A retrospective analysis of patients with at least one <italic>Nocardia</italic> spp. isolation in respiratory samples was performed. PN was defined as isolation of <italic>Nocardia</italic> spp. associated with clinical and radiological findings and NC as occasional isolation of <italic>Nocardia</italic> spp., without clinical or radiological manifestations. Patients with PN and NC were compared and a survival analysis was performed. <bold>Results:</bold> All 71 patients identified had ≥1 pre- existing CLD (64.8% male, mean age 67.6+/-11.2 years). PN was diagnosed in 19 patients and NC assumed in 52. PN patients were significantly more symptomatic and with frequent chest CT findings (p <0.001). During follow-up, PN patients had a significant clinical worsening (p<0.001), with associated decline in FVC (p=0.005) and FEV1 (p=0.033) after 12 months. All PN patients were treated. Twelve patients died, 31.6% with PN vs. 11.5% with NC (p=0.046). No death was directly related to nocardiosis. Immunosuppression and PN diagnosis were associated with shorter survival. <bold>Conclusions:</bold> NC is frequent in CLD patients. In this study, PN was associated with clinical and functional deterioration making the correct diagnosis important to institute early appropriate treatment. Further studies are needed to better guide clinical practice.