Tuberculosis (TB) is still one of the most important infectious diseases in India, but not everyone who has TB germs in the body is actually “suffering from TB.” Some people have latent TB, where germs are sleeping and cause no symptoms, while others have active TB, where germs are multiplying and making them sick. People often get confused between these two stages, worry about infection risk, and are unsure why doctors sometimes treat even when there are no symptoms.
This guide explains the difference between latent and active TB in simple language, how each is diagnosed and treated, and what patients and families in India need to know to protect themselves and others.
What Is Tuberculosis (TB)?
- TB is an infectious disease caused by the bacterium Mycobacterium tuberculosis.
- It most commonly affects the lungs (pulmonary TB) but can also involve lymph nodes, spine, brain, kidneys, intestines, and other organs (extra‑pulmonary TB).
- TB spreads through the air when someone with active lung TB coughs, sneezes, laughs, or speaks, releasing tiny droplets.
After germs enter the body, one of two things can happen: the immune system controls them (latent TB) or they grow and cause illness (active TB).
Latent TB vs Active TB: The Core Difference
Latent TB infection (LTBI)
- TB germs are present in the body but are inactive (sleeping).
- The immune system keeps them under control and walls them off.
- There are no symptoms, the person feels well, and cannot spread TB to others.
Active TB disease
- TB germs are actively multiplying, damaging tissues.
- The person has symptoms (often slowly progressive) and may spread TB to others if the lungs or airways are involved.
About 5–10% of people with latent TB will develop active TB at some point in life, with higher risk in those with weak immunity.
Key Differences at a Glance
| Feature | Latent TB Infection | Active TB Disease |
| Germ activity | Present but dormant | Actively multiplying and damaging tissues |
| Symptoms | None; person feels normal | Usually present: cough, fever, weight loss, etc. |
| Infectious to others | No | Often yes (especially with lung TB) |
| Chest X‑ray | Normal or minor changes | Usually abnormal in pulmonary TB |
| Sputum (mucus) test | Negative for TB bacteria | Often positive for TB bacteria |
| Treatment goal | Prevent future disease | Cure current disease & stop spread |
What Exactly Is Latent TB?
When someone inhales TB germs, the immune system tries to control them. If it succeeds, the germs remain “walled off” but alive inside the body.
Characteristics:
- No cough, no fever, no weight loss.
- Person is not contagious.
- Only clue is a positive TB skin test or TB blood test.
- Chest X‑ray is usually normal and sputum tests are negative.
Latent TB is common in countries with high TB burden like India; many healthy adults may carry TB germs unknowingly.
What Is Active TB?
Active TB means the germs have broken through immune control and are multiplying. This can happen soon after first infection or years later if immunity weakens.
Common symptoms of active pulmonary TB (lungs):
- Cough lasting more than 2–3 weeks.
- Coughing up mucus or blood.
- Chest pain or pain when breathing/coughing.
- Fever, usually low‑grade, often worse in evenings.
- Night sweats (waking up with wet clothes or bedding).
- Loss of appetite and unexplained weight loss.
- Fatigue, weakness, and feeling generally unwell.
Active TB outside the lungs (extra‑pulmonary TB) may cause:
- Swollen lymph nodes (neck, armpit, groin).
- Back pain, deformity (spinal TB).
- Headache, vomiting, confusion (TB meningitis).
- Abdominal pain, diarrhoea or swelling (intestinal TB).
- Urinary symptoms or blood in urine (kidney TB).
People with any of these unexplained symptoms, especially with TB exposure or living in India, should be evaluated promptly.
Who Is at Higher Risk of Developing Active TB from Latent TB?
Only a minority with latent TB develop active disease; risk increases when immunity is weak.
High‑risk groups include:
- People with HIV infection.
- Patients on long‑term steroids or other strong immune‑suppressing medicines (for cancer, transplants, autoimmune diseases).
- People with diabetes, chronic kidney disease, or severe malnutrition.
- Very young children and elderly persons.
- Smokers and heavy alcohol users.
- Close household contacts of someone with active pulmonary TB.
In such people, doctors often strongly recommend preventive treatment for latent TB.
How Are Latent and Active TB Diagnosed?
Diagnosing Latent TB
Doctors rely on:
- TB skin test (Mantoux test / tuberculin skin test)
- A small amount of purified protein (PPD) is injected under the skin.
- The size of swelling after 48–72 hours is measured.
- TB blood tests (interferon‑gamma release assays – IGRA)
- Measure immune response to TB proteins in a lab.
If either test is positive and there are no symptoms, normal chest X‑ray, and negative sputum, the person is usually considered to have latent TB.
Diagnosing Active TB
To diagnose active TB, doctors look for evidence of disease, not just infection:
- Clinical symptoms – prolonged cough, fever, weight loss, etc.
- Chest X‑ray or CT scan – changes in lungs suggestive of TB.
- Sputum tests –
- Microscopy for acid‑fast bacilli.
- Culture (grows TB germs; confirms diagnosis, but takes weeks).
- Molecular tests (e.g., PCR‑based) that detect TB DNA and drug resistance.
For extra‑pulmonary TB, samples from affected organs (lymph node biopsy, fluid tapping, etc.) may be tested.
Why Treat Latent TB If There Are No Symptoms?
Even though latent TB is silent, the germs can “wake up” later, especially when immunity drops. Treating latent TB:
- Greatly reduces the chance of developing active TB later in life.
- Is especially important in high‑risk individuals (HIV, close contacts, immunosuppressed).
- Helps reduce TB burden in the community over time
Preventive treatment regimens are usually shorter and milder than full courses for active TB.
Treatment: Latent TB vs Active TB
Treatment of Latent TB Infection
- Uses 1 or 2 medicines for several months (exact regimen depends on guidelines and patient factors).
- Goal: kill sleeping germs before they cause disease.
- Taken under supervision with periodic tests to ensure safety (especially liver function).
People must complete the full course, even though they feel completely normal.
Treatment of Active TB Disease
- Requires combination therapy with multiple drugs (usually 4 drugs initially) for at least 6 months or longer, depending on site and drug sensitivity.
- Directly observed treatment strategies may be used in TB programmes to ensure adherence.
- Treatment must be strictly completed to:
- Cure the patient.
- Prevent relapse.
- Prevent drug‑resistant TB, which is harder and longer to treat.
Stopping TB medicines early or taking them irregularly is one of the main reasons for drug‑resistant TB.
Can Someone with Latent TB Infect Others?
- No. People with latent TB do not spread TB because germs are inactive and not being coughed out.
- Only people with active pulmonary (lung) or laryngeal TB typically spread infection through droplets.
- Once active TB patients start effective treatment, they usually become much less infectious within a few weeks, though the full course must still be completed.
Living with Latent TB: What Patients Should Know
- It does not mean you have “full TB disease,” but it does mean TB germs are in your body.
- You can live a completely normal life, go to work, school, and be with family.
- You are not a danger to others.
- However, you should:
- Discuss preventive treatment with your doctor.
- Inform future doctors about your latent TB if you ever need immunosuppressive therapy.
- Watch for TB symptoms over the years and seek early evaluation if they appear…
Prevention of TB in the Community
- Early detection and full treatment of active TB cases.
- Screening and preventive therapy in close contacts and high‑risk groups.
- BCG vaccination in infancy (helps prevent severe forms like TB meningitis in children).
- Good ventilation, cough etiquette, and using masks in high‑risk settings.
- Addressing risk factors such as diabetes, malnutrition, smoking, and overcrowded housing.
FAQs
1) If my TB skin test is positive but my chest X‑ray is normal, do I have TB?
A positive TB skin or blood test with a normal chest X‑ray and no symptoms usually means latent TB infection, not active disease. You are not sick and not infectious, but TB germs are in your body. Doctors may recommend preventive medication to lower your future risk of developing active TB, especially if you have health conditions that weaken immunity.
2) Can latent TB turn into active TB many years later?
Yes. TB germs can remain dormant for years or even decades. If your immune system becomes weak later—due to age, diabetes, HIV, kidney disease, cancer treatment, or steroids—latent TB can reactivate and become active TB. This is why preventive treatment and lifelong awareness of TB symptoms are important if you know you have latent TB.
3) How do I protect my family if I am diagnosed with active TB?
First, start and strictly follow the full TB treatment prescribed. This rapidly reduces your infectiousness. Ensure good ventilation at home, cover your mouth and nose while coughing, and wear a mask as advised. Your close contacts (family members, people living in the same house) should be screened for TB, and some may be