Atypical TB is caused by a group of bacteria which belong to Mycobacteria species other than tuberculosis (hence also known as MOTT or non-tuberculous mycobacteria). Common examples of these groups of bacteria include Mycobacterium avium intra-cellulare, M. ulcerans, M. scrofulaceum, etc. These organisms can be present in the environment (soil, water, etc) and disease by these agents is more common in patients with either reduced immunity, or pre-existing disease (chronic lung disease). The infection may manifest as a pulmonary (chest), intestinal, lymph node or skin disease. Recurrence due to relapse or reinfection, of the disease can occur when immunity falls (e.g. cancer, radiation, HIV infection, immuno-suppressive therapy etc). Disease due to active atypical mycobacterial infection is treated with a combination of at least two drugs, of which the first one is often clarithromycin or azithromycin. Many experts prefer ethambutol as the second drug. Some clinicians have added a third or fourth agent from the following list: clofazimine, rifabutin, ciprofloxacin, or amikacin. I suggest you refer to a physician experienced in the management of TB for appropriate management advice.