Tuberculosis (TB) is a centuries-old disease that many believe is now relegated to the slums of impoverished countries in Africa and Asia.
But while developing countries bear the brunt of new infections, TB is still one of the world's deadliest illnesses, killing 1.4 million people in 2011 alone. One out of every three people alive today carries Mycobacterium Tuberculosis, the germ that causes the illness.
"There's no question that if you're poor, then you're much more likely to have tuberculosis. But because TB is an airborne disease, TB anywhere is TB everywhere," says Dr Peter Small from the Bill and Melinda Gates Foundation.
The disease is most infectious in congested communities with poor access to quality nutrition and hygiene, conditions that are rife in India.
It spreads through microscopic droplets from a TB-infected patient's cough that travel through the atmosphere and can be inhaled by anyone in the vicinity.
Once inside the body, the immune system walls off the bacteria to prevent it from multiplying. And that is where it lays waiting, sometimes for decades or even a lifetime, until the perfect opportunity arises.
When the immune system of a TB-infected person becomes compromised through stress, an illness like HIV or malnutrition, the bacteria seizes the moment and multiplies, usually in the lungs. It then moves through the body via the blood stream.
If left untreated, a patient slowly loses weight, suffers from chills and fevers, and ultimately dies, after potentially infecting up to 15 more people.
For the past 40 years, the same medicines has been used to treat TB. As recommended by the World Health Organisation (WHO), patients are given a first line cocktail of drugs for about six months. If they fail to respond, a second more aggressive line of treatment begins - a gruelling two-year regime of combination medication including injections. But what happens when the strongest treatments for TB fails to cure the patient?
That is the predicament that faced Dr Zarir Udwadia and his colleagues at Mumbai's Hinduja Hospital. They were baffled by a number of patients whose laboratory tests showed resistance to all 12 drugs then used to treat the illness - patients they described as infected with a 'Totally Drug Resistant (TDR)' strain of the bacteria.
"The first patient I will never forget because she was a lady who came to us from Uttar Pradesh (State). She trekked across two major states in India at distances 1000km apart. Think about how soul-destroying it must be to have five years of treatment with multiple providers - private practise, public practise -and find that you're getting worse, not better." says Dr Udwadia.
But when the Mumbai doctors flagged the problem, the government rejected their findings. They accused the doctors of being alarmist and raised questions about the quality of their laboratory. The WHO also refused to recognise the term TDR, arguing that the patients may respond to any new drugs released in the market.
But privately, health workers admit that drug resistant strains of TB are spreading in India.
The WHO estimates there are 66,000 cases of multi-drug resistant TB nationwide but the real figure could be much higher because people are being misdiagnosed with illnesses like typhoid, malaria and standard TB before doctors realise they have a drug-resistant strain of the disease.
This forces doctors to play a dangerous guessing game when treating people because if a patient has drug-resistant TB from the beginning, treatment for anything else may help strengthen the bacteria.
But beyond the science of the illness, India is paying a heavy human cost because of this contagion. The poorest are worst affected, but they are also the least equipped to deal with the devastating impact of the disease.
"Each story is heart-breaking really because these are the young bread-earners of their families. I tear up in my eyes when I talk about it because many of them are going to die, they're going to pass it onto their wives and their children," says Dr Udwadia from Hinduja Hospital in Mumbai.
"They incur huge bills just trying to cure themselves of this problem. They run from pillar to post trying to get treatment, drugs are in short supply and not easily available. And I've seen entire families devastated, wiped out, bankrupt, selling their few poultry, jewellery, [and] properties, in a desperate attempt to cure themselves of this TB."
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