When is pulmonary tuberculosis not tuberculosis and actually a chronic fungal infection?

Around 10-20% of patients diagnosed with pulmonary tuberculosis (PTB) have a chronic fungal lung infection, and others have another lung problem, such as non-tuberculous mycobacterial infection or allergic bronchopulmonary aspergillosis. A smaller number have a co-infection with PTB and chronic lung infection. There are multiple reasons for trying to get the diagnosis right, if only to avoid using unnecessary anti-tuberculous therapy and its potential for toxicity and drug interactions.