Tuberculosis: Understanding Latent Infection, Active Disease, and How Drug Therapy Works

Most people who get infected with tuberculosis never get sick. That’s not a myth-it’s science. The bacteria that cause TB, Mycobacterium tuberculosis, can live quietly in your lungs for years, even decades, without causing a single symptom. But if your immune system weakens, those same bacteria can wake up, multiply, and turn into a life-threatening illness. This is the quiet, dangerous duality of tuberculosis: one infection, two very different outcomes.

What Is Latent TB Infection?

Latent TB infection means the bacteria are alive but asleep. Your body has locked them away inside tiny immune cell clusters called granulomas. You feel fine. You don’t cough. You can’t spread it to anyone. But if you take a skin test or blood test (called a TST or IGRA), it will show up as positive. That’s how doctors know you’ve been exposed.

According to the CDC, about one-quarter of the world’s population has latent TB. That’s nearly 2 billion people. Most will never develop active disease. But for 5% to 10% of those infected, the bacteria will reactivate at some point in their lives. The risk jumps dramatically if you have HIV, diabetes, kidney disease, or are on immunosuppressive drugs like steroids or biologics for autoimmune conditions. People with untreated HIV are up to 20 times more likely to develop active TB.

Latent TB doesn’t show up on a chest X-ray. No fever. No weight loss. No night sweats. It’s invisible unless you test for it. That’s why public health programs focus on screening high-risk groups-people who came from countries with high TB rates, healthcare workers, prison inmates, and those living in crowded shelters.

When Latent TB Turns Active

Active TB disease is when the bacteria break free from their immune prisons and start multiplying. They destroy lung tissue, spread through the air, and make you sick. The symptoms don’t come on suddenly. They creep in over weeks: a cough that won’t quit, fatigue that doesn’t lift, night sweats so heavy you need to change your pajamas, and unexplained weight loss-even if you’re eating normally.

If the infection spreads beyond the lungs (called extrapulmonary TB), it can affect your spine, brain, kidneys, or even your bones. But most cases start in the lungs. That’s why a persistent cough lasting more than three weeks is a major red flag. Some people cough up blood. Others feel chest pain when they breathe or cough.

Active TB is contagious. When someone with active lung TB coughs, sneezes, or talks, they send tiny droplets into the air. You don’t need to be right next to them-just sharing the same enclosed space for hours increases your risk. That’s why TB spreads easily in prisons, homeless shelters, and crowded housing.

Diagnosis isn’t just about symptoms. Doctors need proof. A chest X-ray often shows spots or cavities in the lungs. But the gold standard is finding the bacteria in sputum. That’s done through a culture-growing the bacteria in a lab, which takes weeks-or faster molecular tests like NAAT that detect TB DNA in hours.

Drug Therapy for Latent TB

Treating latent TB isn’t about curing symptoms-it’s about prevention. The goal is to kill the dormant bacteria before they wake up. The most common treatment is isoniazid (INH), taken daily for nine months. It’s cheap, effective, and has been used for over 60 years. But sticking to it for that long is hard. People forget. They feel fine. They stop taking it. And that’s how drug resistance starts.

That’s why shorter regimens are now preferred. The CDC and WHO recommend a 3-month course of weekly isoniazid and rifapentine (3HP). It’s taken under direct observation-someone watches you swallow the pills. This improves completion rates from around 60% to over 85%. Another option is rifampin alone for four months. Both are safer for the liver than long-term isoniazid.

Not everyone with latent TB needs treatment. Doctors weigh the risks: your age, your immune status, your exposure history, and your risk of side effects. For example, a healthy 25-year-old who was exposed once might not get treatment. But a 60-year-old with diabetes and recent exposure? Treatment is strongly recommended.

Drug Therapy for Active TB

Active TB is a medical emergency. Left untreated, it can kill. But with the right drugs, it’s curable. The standard first-line treatment is called RIPE therapy: rifampin, isoniazid, pyrazinamide, and ethambutol. These four drugs are taken together for the first two months to smash the bacteria from every angle.

After two months, you drop pyrazinamide and ethambutol. You keep rifampin and isoniazid for another four to seven months. That’s six to nine months total. It’s long. It’s intense. And it’s non-negotiable.

Why so many drugs? Because TB bacteria are sneaky. If you take only one or two, the strongest ones survive and multiply. That’s how drug-resistant TB forms. Multidrug-resistant TB (MDR-TB) doesn’t respond to the two most powerful drugs-isoniazid and rifampin. Treating MDR-TB takes 9 to 20 months, uses more toxic drugs, and costs up to 100 times more.

Directly Observed Therapy (DOT) is the standard of care. A nurse, community health worker, or even a family member watches you take every pill. This isn’t about control-it’s about saving lives. Studies show DOT cuts treatment failure and drug resistance by half.

Side effects are real. Isoniazid can damage your liver. Rifampin turns your urine orange. Pyrazinamide can cause joint pain. That’s why regular blood tests are required. If you feel nauseous, yellow-eyed, or unusually tired, tell your doctor immediately.

Why TB Still Kills Millions

Despite having effective treatments for over 70 years, TB killed 1.3 million people in 2022, according to the WHO. Why? Because access isn’t equal. In low-income countries, people wait weeks to get tested. Diagnostic tools are scarce. Medications run out. DOT programs are underfunded.

Even in wealthy countries like the U.S., TB clusters in marginalized communities. Foreign-born individuals make up over 70% of cases. Homelessness, incarceration, and poverty create perfect conditions for spread. And stigma keeps people silent. Many don’t go to the doctor because they fear being isolated or deported.

The biggest missed opportunity? Not treating latent TB. Every untreated latent case is a ticking bomb. If we screened and treated just 10% of the world’s latent infections, we could prevent hundreds of thousands of active cases every year.

What’s New in TB Care?

Science is catching up. New tests can now detect latent TB with more precision, distinguishing between recent infection and old exposure. Researchers are testing shorter active TB regimens-four months instead of six-with promising early results. A new drug called pretomanid, approved in 2019, is now part of treatment for MDR-TB, cutting therapy time from 18 to 6 months.

There’s also hope in vaccines. The BCG vaccine, used since the 1920s, protects children from severe forms of TB but doesn’t stop lung infection in adults. New candidates are in phase 3 trials, and early data suggests some may reduce infection rates by up to 50%.

But the biggest breakthrough isn’t a drug or a vaccine. It’s recognizing that TB isn’t just a medical problem-it’s a social one. You can’t cure TB without housing. You can’t stop transmission without food security. You can’t end stigma without education.

What You Need to Know

If you’ve been exposed to someone with active TB, get tested. Even if you feel fine. A simple skin or blood test can save your life.

If you’re diagnosed with latent TB, take your medicine. Don’t wait until you feel sick. The bacteria won’t warn you.

If you have active TB, follow your treatment plan. No skipping doses. No stopping early. Your life-and the lives of those around you-depend on it.

Tuberculosis is not a disease of the past. It’s a disease of inequality. And it’s still here. But it’s not unstoppable. With testing, treatment, and compassion, we can end it.