**4. Conclusions**

In patients with silicosis and symptoms that sugges<sup>t</sup> infection, mycobacterial disease should be considered in the differential diagnosis. *M. chimaera* infection is characterized by ambiguous symptoms. Moreover, the course of the disease, as in our case, can be prolonged. Diagnosis requires using modern genetic techniques and not all tests available in various laboratories are specific enough. Moreover, there is no treatment with proven effectiveness and even proceeding according to the guidelines, as it was in our patient, eradication is not always achieved. The disease has a poor prognosis despite the treatment. Detailed analysis of different patients' managemen<sup>t</sup> could lead to the development of diagnostic and therapeutic recommendations for *M. chimaera* infection.

**Author Contributions:** E.Ł., writing—original draft preparation; I.S.-S., M.S. and K.L., writing—review and editing; M.B. and K.Z., data collection, patient's medical care; L.J., radiological scans preparation and description; E.A.-K., microbiological tests performance; W.T., supervision. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institution Review Board Statement:** The study was approved by the Ethics Committee of the National Research Institute of Tuberculosis and Lung Diseases (KB-64/2018, 14 December 2018) as a part of research on mycobacterial diseases in humans.

**Informed Consent Statement:** The patient died before publication was started. Written informed consent to publish this paper has been obtained from the patient's family member.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
