Nocardia colonization in contrast to nocardiosis: a comparison of patients’ clinical characteristics

Information on Nocardia colonization of the lower respiratory tract is scarce. The current study is aimed at comparing clinical characteristics between individuals with Nocardia colonization and those with nocardiosis. All patients with Nocardia isolation between 2007 and 2018 at a tertiary hospital in Israel were included. Nocardia isolation was based on biochemical tests together with phenotypic susceptibility and resistance patterns until 2011 and on matrix-assisted laser desorption/ionization time-of-flight mass spectrometer from 2012. We defined nocardiosis as a clinically evident infection related to the isolation of the bacteria, which required antibiotic therapy. We defined colonization as Nocardia isolation with no clinical evidence of disease. The medical charts of all included individuals were independently reviewed by an infectious disease specialist to ensure adequate classification. Logistic regression models were fitted to compare clinical characteristics between the groups. Fifteen (20%) of the 75 Nocardia isolations met the criteria for colonization. Of those, 13 (87%) had background illnesses. Having a chronic pulmonary disease was associated with increased likelihood of Nocardia colonization, in contrast to nocardiosis (adjusted odds ratio [OR] 4.06, 95% confidence interval [CI] 1.06–15.48, p = 0.040), while an inverse association was found with corticosteroid therapy (adjusted OR 0.21, 95% CI 0.06–0.74, p = 0.015). Nocardia colonization of the lower respiratory tract accounts for a substantial proportion of all Nocardia isolations. Individuals colonized with Nocardia typically have chronic pulmonary disease and are less frequently treated with corticosteroid than patients with nocardiosis.