**4. Conclusions**

This paper addresses the important social and epidemiological problems of contact tracing between family members and the active detection of tuberculosis infection sources in households with young children. It is known that such children are exposed to a small number of potential sources of infection, and the time of potential TB transmission is limited. Yet, the level of source-case detection in many populations worldwide remains low, implying a missed opportunity in TB eradication. The morbidity and mortality of tuberculosis in children reflect the quality of surveillance of transmission from adults. The effective control of this infectious disease requires, first of all, a careful estimate of morbidity and mortality in children. Professional medical care should be provided not only to paediatric patients diagnosed with tuberculosis, but also their close family.

The described case implies that currently TB control programs should prioritize the development and implementation of guidelines on chemoprophylaxis in patients with XDR-TB, especially in young children infected after contact with their family members.

**Author Contributions:** Conceptualization, M.K. and E.A.-K.; methodology, M.K., K.B., K.K., J.S.-S., W.P.-O. and A.P.; formal analysis, M.K., K.K. and W.P.-O.; investigation, M.K., K.B., K.K. and E.A.-K.; writing—original draft preparation, M.K. and W.P.-O.; writing—review and editing, E.A.-K., J.S.-S., W.P.-O. and A.P.; funding acquisition, E.A.-K. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by National Science Center, gran<sup>t</sup> number 2019/35/B/NZ7/00942.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study. Written informed consent has been obtained from the patient(s) to publish this paper.

**Data Availability Statement:** The results of the presented research are archived in the documentation of hospitals where mother and daughter were treated: Department of Tuberculosis and Lung Diseases, Specialist Hospital in Prabuty, Kuracyjna 30, 82-550 Prabuty, Poland and Department of Allergology, Immunology and Lung Diseases, The Maciej Płazy ´ ˙ nski Polanki Children's Hospital, Polanki 119, 80-308 Gdansk, Poland. Microbiological documentation has been archived at the Department of Microbiology, National Tuberculosis and Lung Diseases Research Institute, Plocka 26, 01-138 Warsaw, Poland.

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