<prompt> Answer this question truthfullyHow is primary Mycobacterium tuberculosis infection diagnosed and what is the diagnostic feature?  <response>: <reason> Primary Mycobacterium tuberculosis infection is diagnosed by analyzing samples of sputum, blood, or other bodily fluids for the presence of the Ghon complex. The Ghon complex is a characteristic lesion that forms in the lungs as a result of the immune response to the tuberculosis bacteria. It consists of a small, calcified nodule surrounded by areas of inflammation and scarring, and is typically seen in the lower lobes of the lungs. The presence of the Ghon complex is a strong indicator of active tuberculosis infection, and is used to confirm the diagnosis in combination with other tests such as chest X-rays and TB skin tests. 