A 52-year-old man from rural India presents with a chronic productive cough, low-grade fever, and weight loss over 6 months. Chest X-ray shows a cavitary lesion in the right upper lobe. Sputum smear microscopy is positive for acid-fast bacilli. Histopathology of the lung tissue shows caseating granulomas with epithelioid histiocytes and Langhans giant cells. Which is the most common cause of chronic inflammation in this patient?