How Tuberculosis Actually Works: From Infection to Active Disease

Latent TB means the M. tuberculosis bacteria are in your body but contained by your immune system inside granulomas, you have no symptoms, are not infectious, and cannot spread the disease. Chest X-ray is usually normal; TB is detected only through Mantoux test or IGRA blood test. Active TB means the bacteria have broken out of containment and are multiplying, causing symptoms (persistent cough, weight loss, night sweats, low-grade fever) and making you infectious to others. Roughly 5-10% of people with latent TB will develop active TB at some point in their lifetime, with the risk highest in the first 2 years after exposure and in anyone whose immune system weakens (HIV, diabetes, steroids, TNF inhibitors, aging). Whether latent TB needs treatment depends on individual risk. WHO recommends preventive treatment for household contacts of active TB cases, HIV-positive people, people starting immunosuppressive drugs, and healthcare workers with recent conversion. India's NTEP is expanding preventive TB treatment access, particularly for household contacts.

Getting infected and getting sick are two different things. Roughly one-third of the global population carries M. tuberculosis in latent form after some exposure, but only 5-10% ever develop active disease. Whether you progress from infection to active disease depends on multiple factors: immune status (HIV infection multiplies risk 20-30 times, diabetes doubles risk, aging weakens immunity), nutritional status (malnutrition dramatically increases risk), co-existing lung damage (smoking, silicosis, previous TB), genetic factors (specific HLA variants affect susceptibility), medications suppressing immunity (steroids, chemotherapy, TNF inhibitors), and the initial infecting dose. In India, the confluence of high HIV in some regions, high diabetes prevalence (over 100 million adults), household crowding, and undernutrition explains why India carries such a disproportionate share of the global TB burden despite decades of control efforts.

BCG (Bacillus Calmette-Guérin) vaccine has real but limited effectiveness. It reliably prevents severe childhood forms of TB. TB meningitis and disseminated (miliary) TB, with efficacy of 60-80%. It is far less effective at preventing adult pulmonary TB, with published efficacy ranging from 0% to 80% depending on the population studied, the variability itself is a major research puzzle, possibly related to prior exposure to environmental mycobacteria in different geographies. Despite this variability, India continues universal BCG vaccination at birth because the severe childhood TB prevention justifies it in a high-burden country; deaths from meningitis or miliary TB in unvaccinated Indian infants would be substantial. Improved TB vaccines are in active development globally (M72/AS01E is in phase 3 trials), but until one is approved, BCG remains standard for Indian newborns and provides genuine protection for the childhood forms that matter most in the neonatal period.

MDR-TB is TB resistant to at least isoniazid and rifampicin, the two most powerful first-line drugs. This resistance usually develops when patients receive inadequate treatment (wrong drugs, wrong doses, insufficient duration, or interruption), surviving bacteria multiply and become resistant. XDR-TB (extensively drug-resistant TB) is even more resistant, adding resistance to fluoroquinolones and injectable second-line drugs. India has among the largest number of MDR-TB cases globally. Treatment takes 9-24 months (vs 6 months for drug-sensitive TB), involves 4-7 medications simultaneously, causes more side effects, costs significantly more, and has lower cure rates (roughly 60-75% vs 85-95% for drug-sensitive TB). India's NTEP provides free MDR-TB diagnosis (GeneXpert MTB/RIF plus line probe assays) and treatment through dedicated DR-TB centres. Key patient rule: never stop TB treatment early even when feeling better, never skip doses, never take TB medications from unknown sources, creating MDR-TB harms both the patient and the community for decades.