Original Article
Clinical characteristics of pulmonary nocardiosis in immunocompetent patients

https://doi.org/10.1016/j.jiac.2016.08.004Get rights and content

Abstract

Pulmonary nocardiosis is a rare but potentially serious infection typically in immunosuppressed patients (ISPs). It is also known to occur in immunocompetent patients (ICPs). However, little is currently known regarding the clinical characteristics and radiographic findings of pulmonary nocardiosis specifically in ICPs. In this study, 30 patients with pulmonary nocardiosis were identified and 10 were considered to be colonized. Of all patients with pulmonary nocardiosis, 12 patients were ICPs and 18 were ISPs. Although half of ISPs were infected by Nocardia nova, ICPs were affected by various Nocardia species. Compared with ISPs, chest CT findings of ICPs showed a higher prevalence of bronchiectasis (67% vs 6%, p < .01) and centrilobular nodular opacities (67% vs 11%, p < .01), both of which are often seen in pulmonary nontuberculous mycobacterial disease. Additionally, nontuberculous mycobacterium was isolated from 6 of 21 ICPs with positive Nocardia species culture. Therefore, we recommend that physicians carefully differentiate pulmonary nocardiosis from pulmonary nontuberculous mycobacterial disease in ICPs.

Introduction

Nocardia species are weakly acid-fast bacteria and they are found in soils, water, and other organic matter worldwide [1]. Pulmonary nocardiosis is a well-described infectious disease in immunosuppressed patients (ISPs), but it can also occur in immunocompetent patients (ICPs). ICPs with pulmonary nocardiosis mostly have underlying chronic lung diseases such as chronic obstructive pulmonary disease (COPD) [2] and bronchiectasis [3]. However, the clinical and radiographic features of ICPs with pulmonary nocardiosis are not yet well-documented.

Nontuberculous mycobacteria (NTM) are also acid-fast bacteria and common natural inhabitants of soil and water throughout the world. Nontuberculous mycobacterial disease usually presents as a pulmonary disease in ICPs but can present as a disseminated disease especially in human immunodeficiency virus (HIV)-infected patients. Moreover, NTM were reported to be isolated from respiratory specimens of ICPs with pulmonary nocardiosis [4], [5], suggesting that NTM and Nocardia sp. may be related in pulmonary infections. In this study, we compared clinical characteristics, radiological findings, microbiological findings and treatment outcomes of pulmonary nocardiosis between ICPs and ISPs, and also investigated an association of Nocardia species with NTM in ICPs.

Section snippets

Patients and definitions

This study was a retrospective analysis that was undertaken of patients diagnosed with pulmonary nocardiosis over an eleven-year period at the Chiba University Hospital, Japan. Cases of pulmonary nocardiosis were identified with the clinical microbiology laboratory database for specimens collected between 2004 and 2014. Pulmonary nocardiosis was defined by the presence of clinical and radiographic manifestations and radiological improvement following appropriate treatments for Nocardia species

Characteristics of the individuals (Table 1)

Thirty patients with pulmonary nocardiosis were identified. Among them 12 (40%) were ICPs (8 males and 4 females) while 18 (60%) were ISPs (10 males and 8 females), 4 of whom had disseminated nocardiosis. Mean age of ICPs (69.0 years) was higher than that of ISPs (54.6 years). Additionally, 10 were considered colonized, nine (90%) of whom were immunocompetent and one was immunosuppressed. In ICPs with pulmonary nocardial infections, underlying lung structural abnormalities were common

Discussion

Pulmonary nocardiosis is a rare but potentially serious infection typically in ISPs. The use of immunosuppressant agents (e.g. due to solid organ transplantation and hematopoietic stem cell transplantation) and corticosteroid therapies is the main risk factors for nocardial infection [10]. However, it is also known to occur in ICPs, especially with underling pulmonary diseases such as COPD and bronchiectasis. These preexisting structural abnormalities of the lung cause a respiratory immune

Conflict of interest

All authors declare no conflict of interest in this work.

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