Tuberculosis has killed more people than any other disease in history. Last year, 1.5 million people died from TB and 10 million more acquired it. A shocking one-quarter of the world’s population is infected. That’s not much better than 1993, when one-third of the world was infected and the World Health Organization declared TB a global emergency. We are losing the battle.

Earlier this month, experts gathered in Hyderabad for the 50th Union World Conference on fighting the disease. When the first such gathering was held in 1867, TB was the leading cause of death in industrialised nations. Today, it still ranks in the top 10 worldwide. Why, despite all the progress in medicine and public health over the past 150 years, is TB still the most common and lethal of all infectious diseases?

First, TB has a singular capacity for contagion. When someone with active TB coughs or sneezes, they launch respiratory droplets containing the bacteria into the air. These droplets can stay suspended for hours, turning shared spaces – homes, schools, public transport, hospital waiting rooms – into transmission hot spots. And unlike some diseases, such as measles, which can be caught only once, this “smart” pathogen can cause disease multiple times.

But easy as TB is to catch, it is hard to diagnose. Once someone is infected, either the body’s immune system defeats it, it becomes dormant (latent TB) or it develops into the active disease.

The chief symptoms – cough, fever, and weight loss – come on slowly and are common to many other diseases.

Most diagnostic tests are more than a century old and not very effective. Sputum microscopy has been used since Robert Koch discovered Mycobacterium tuberculosis in 1882. It only picks up half the cases of active TB. The skin, or Mantoux, test, also dating from the 19th century, which can detect latent TB, doesn’t pick up anything for two months after exposure.

Modern, more accurate tests are prohibitively expensive. Bacterial culture, the gold standard, takes weeks for results. False negatives or long waits delay getting people into treatment; when they are, it takes just 72 hours for them to stop being infectious.

We need much better detection. And better methods for diagnosing younger children who may have to suffer their stomach contents being collected to mine swallowed sputum.

Untreated, TB has a 70% fatality rate among HIV-negative people. Treated, that drops to 5%.

But the shortest treatment takes six months, using drugs developed more than 50 years ago. Adverse side effects, out-of-pocket costs, and loss of work lead some people to stop treatment, contributing to the rise of drug-resistant strains.

Drug-resistant TB requires treatment with second-line drugs that have seriously toxic side effects, such as hypothyroidism, hearing loss, skin pigmentation and kidney failure. When people stop treatment early, it creates a vicious cycle – interrupted treatment breeds drug resistance, making treatment more difficult, with higher rates of failure and death. The success rate for treatment of multi-drug resistant TB was 56% in 2018. For extensively drug-resistant strains it was just 39%.

Drug-resistant tuberculosis is one of our most urgent and difficult challenges. In 2018, of the estimated half a million people who developed multi-drug resistant TB, only one in three was in treatment. To make matters worse, drug-resistant TB is increasingly spread by direct human-to-human transmission. So people are catching strains that are already resistant.

We urgently need to develop new, better and cheaper drugs. More than 20 are currently in clinical trials.

TB remains a key symptom of physical and social vulnerability. Only 10% of infected people develop the active disease, meaning our natural defences are usually more effective than drugs unless immune systems are weak or compromised, such as in young children, or people with diabetes, untreated HIV or malnutrition.

Even the announcement from Hyderabad of a new vaccine shows the progress still needed. Currently the TB vaccine, dating from 1921, does not protect people for life. A new vaccine promises improvements, but is only effective about 50% of the time.

TB is a disease of the vulnerable, which may be why so little has been done to modernise the fight against it. It spreads most easily in conditions of poverty, with people crowded together in poorly ventilated places. It is symptomatic of a failure to ensure everyone has access to healthcare and is free from poverty and poor hygiene.

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These are society’s failures, but the stigma often falls on individuals. Society tends to shun TB patients and the medical establishment subordinates their individuality to the demands of fighting the disease. Moreover, the costs of treatment can be catastrophic, driving families further into poverty.

It is time to step up the effort. That requires better-targeted investment and greater attention to the conditions that breed TB. We need treatment strategies that support and empower patients to manage their own disease.

The best protection is a robust immune system. The link between TB and HIV – affecting 38 million worldwide – is widely known. The link between TB and diabetes, which affects half a billion people, is not. Any condition that suppresses the immune system – including kidney disease and cancer – puts people at increased risk, as does smoking, alcohol, and substance abuse.

We need a holistic approach to address the social, physical and clinical drivers. Strong healthcare is particularly important, as is protecting people from catastrophic health costs that destroy livelihoods, force patients off treatment, and accelerate drug resistance.

Traditionally, the approach has been to stamp out disease to make people healthier. Ultimately, making people healthier is the best way to stamp out TB.