Case Report First report of solitary cavitation nodules in the lungs with Mycobacterium canariasense

Introduction: Mycobacterium canariasense is a relatively rare and rapidly growing nontuberculous mycobacterium (NTM) infection. Case report: This case report describes a 36-year-old man with a Canariasense infection in the lung with solitary cavitation nodules located subpleural on CT scan, for which the final diagnosis was made by metagenomic next-generation sequencing (mNGS) of bronchoalveolar lavage fluid (BALF-mNGS). It was successfully treated with levofloxacin and amikacin. Conclusions: This experience is instructive because clinical diagnostic and CT imaging characteristics and treatment strategy guidelines for pulmonary infections caused by M. canariasense have not yet been established.


Introduction
Nontuberculous mycobacterium (NTM) lung disease previously appeared to be uncommon with low physician awareness, mainly due to limitations in diagnostic techniques.The exact cause of the increase in NTM disease is unclear.Currently, reports of NTM are on the rise globally [1] due to population aging and comorbidities, doctor attention, and advances in laboratory techniques for diagnosing this disease.NTM are mycobacteria other than tuberculous (MOTT) [2], with more than 200 species identified to date.M. canariasense is considered to be an environmental pathogen and may act as an opportunistic pathogen.According to the literature, it was first isolated from clinical specimens in Spain in 2004 and has since been isolated from Iran hospital water in 2011 [3].It was also detected in the Spanish water supply in 2016 [4].

Case presentation
A 36-year-old man was admitted to our institution with a physical examination.His temperature was 36.7°C,pulse 90 beats per minute, blood pressure 132/77 mmHg, and respiratory rate 19 breaths per minute.The patient had no cough, no phlegm, no fever, no chest tightness, no shortness of breath, no chest pain, no hemoptysis, and no notable recent weight loss.He denied a history of hypertension and diabetes.He denied hepatitis, tuberculosis, and other infectious history.He denied surgical history, denied history of other trauma, and denied history of blood transfusions.He denied any history of drug or food allergies.He had a smoking history of approximately 3 years, 6-7 cigarettes/day.He denied a history of alcohol abuse.Male tumor indicators were negative, all inflammatory indicators in routine blood tests were negative, and CD4+ T cells, CD8+ T cells, and NK cells were normal.Cryptococcus clip membrane antigen, Aspergillus IgG, DNA of Bacillus tuberculosis sputum, X-pert of sputum, and sputum culture of common bacteria were negative.The COVID-19 nucleic acid test was negative.
The patient underwent sputum mycobacterium culture, common bacterial culture testing, and drug sensitivity testing before hospitalization, and the results were negative.The initial diagnosis was pulmonary infection, anti-infective treatment with cefixime, and there was further diagnosis by bronchoscopy on the third day of hospitalization.BALF-Xpert was negative, BALF-TBDNA was negative, BALF-GM was negative, and the tracheoscopy brush and BALF smear for acid-fast bacilli were negative.BALF culture of mycobacteria, common bacteria, and drug sensitivity were also negative.Tracheoscopy brush and BALF smears for shedding cells did not reveal heterotropic cells.
However, the BALF-NGS report was M. canariae, sequence number 27.The CT scans before and after treatment are shown in Figure 1.

Discussion
A review of the patient history showed that the patient had normal immunity, no special epidemic history, and negative NTM sputum culture.However, BALF-mNGS was positive.NTMs are ubiquitous in the environment.
The increasing incidence and mortality of NTM worldwide over the past few decades is both a new clinical challenge and a public health issue [1].In some special circumstances, NTM can invade the human body through the respiratory tract, gastrointestinal tract, skin, and other pathways.Its pathogenic process is similar to that of tuberculosis, but the molecular mechanism of the body's anti-NTM immune response has not been fully clarified [5,6].In recent years, due to the increasing incidence of NTM in immunocompromised and immunonormal patients, attention to infections caused by NTM has become quite important [7].The case we encountered is relatively rare.In China, CT examination of small pulmonary nodules is quite popular and most patients are anxious, which needs to be addressed by clinicians.We found strong diagnostic evidence for the infectious disease that was considered first, and it was treated successfully.Although few reports have demonstrated the efficacy of levofloxacin and amikacin [8][9][10] against M. canariasense, diagnostic and treatment methods for this pathogen have yet to be fully elucidated.The successful treatment of this case can be used as a reference experience.
M. canariasense is a rapidly growing nontuberculous mycobacteria (RGM) [11].RGMs are environmental organisms that can behave as contaminants as well as pathogens [8].According to the literature [10], the 2019 Iranian medical records provide published reports on the treatment of M. canariasense pulmonary disease.The phenotypic and genotypic characteristics of isolates of this strain were determined in accordance with guidelines from the American Thoracic Society and the Infectious Diseases Society of America.However, it is essential to accumulate further evidence for diagnosis and treatment.The diagnosis of NTM itself is difficult, and rare NTM is not easy to diagnose.While we appreciate CT imaging as a direct indication of lung infection, we also appreciate that mNGS has been a helpful tool in the final diagnosis and can be viewed as the reference standard.
Based on the mNGS and the final treatment results, the diagnosis of M. canariae in this case is considered reliable.There was no evidence of other diseases or pathogens.At present, the clinical features, diagnostic methods, and treatment strategies for M. canariasense respiratory infection are not yet fully elucidated.Awareness of the possibility of this condition is important, and further collection and analysis of suspected cases are mandatory.
Due to earlier bacterial culture techniques, these infections are frequently misdiagnosed and undertreated, and their true prevalence suffers from gross underestimation.With the continuous application of gene testing technology, especially in the central and eastern regions of China with better economic conditions, this technology can be rapidly developed and applied in difficult clinical problems, thus rapidly increasing the diagnosis rate of NTM and carrying out effective antibiotic therapy.

Figure 1 .
Figure 1.The CT scan before and after treatment.