Hein S Seok is a Korean-American documentary filmmaker whose film, Out of Breath, follows a team of international volunteers to North Korea, where they work with local doctors to fight the deadly multidrug-resistant tuberculosis. Here, she writes of witnessing the bonds between the visitors and North Koreans to fight what's been called the isolated country's "first, second and third most serious health issue".

In most US cities, Stephen Linton would be unnoticeable — a white man in his mid-60s, with an average build and greying hair. But not in North Korea.

There, he is the most impossible of figures — an American who is not only fluent in Korean, but the North Korean dialect. And he is helping to treat tuberculosis patients.

I first met Dr Linton in 2010 to interview him for a documentary about humanitarian aid to North Korea, known officially as the Democratic People's Republic of Korea.

He came from a long line of missionaries in Korea and had established the Eugene Bell Foundation, a Christian charity and one of the very few organisations in the world that works directly with the North Korean Ministry of Health.

Despite my grandparents being from North Korea, visiting the country had never crossed my mind. I had been brought up on media stories about nuclear armament and aggression. North Korea was a forbidding place and its people, hostile.

But during the interview, Dr Linton asked: "Would you like to see the country for yourself? What you think you know is not what you will find."

I said yes on the spot.

'It's a very painful way to die'

Getting a visa to North Korea proved to be much more difficult — I waited for two years to become an official member of Eugene Bell's delegation.

My primary role was to film their efforts and tell the story of the North Koreans I met. I joined an international team of volunteers, consisting of a tuberculosis specialist, priests and a historian, who visit North Korea every six months to deliver medicine to a dozen tuberculosis centres.

Patients with MDR-TB can require chemotherapy for up to two years. ( Supplied: Hein S Seok )

Tuberculosis is a disease that spreads through the air and thrives on poverty and malnutrition. It causes a chronic infection in the lungs, slowly liquefying lung tissue and eating into blood vessels.

Patients can die suddenly if their lungs fill with blood or slowly and agonisingly from respiratory failure.

Eugene Bell's medical director KJ Seung told me "at the end of the patients' lives, it's really difficult to watch because you can see them gasping for air".

"It's a very painful way to die because it takes so long.

"But the cruellest thing about tuberculosis is that it is infectious. You don't just die, you actually kill the people you love."

To add to the difficulty, Eugene Bell focuses on a particular strain of tuberculosis that is very resistant to drugs. Multidrug-resistant tuberculosis (MDR-TB) infects half a million people each year worldwide.

Unlike regular tuberculosis, which can be cured in months, MDR-TB requires uninterrupted and expensive chemotherapy for up to two years. The drugs are toxic to humans but weak against MDR-TB, and because of this many people call it the "contagious cancer".

If patients fail to receive their chemotherapy on time, they die.

One of the patients I met was a young girl named Yongsim, who appears in my film. Her father was ill and too feeble to walk on his own, so she carried him on her back to the centre for treatment. They both tested positive for MDR-TB. Her father was in a critical condition, but Yongsim's symptoms were still mild.

Yongsim carried her own father to a treatment centre after he fell ill. ( Supplied: Hein S Seok )

The staff and the sanatorium patients gathered around them, trying to explain that the medicine brought by Eugene Bell was their only hope. But Yongsim's father, thinking he was too far gone, wanted the medicine to be given to someone with a better chance. And Yongsim wanted to go home to take care of her father, giving up her chance to be treated.

When I returned to this centre six months later, I was very happy to find Yongsim sitting among the patients, looking much healthier. Sadly, her father had passed away. She told me she still cried when she thought about how he was not able to get the medicine he needed in time.

She wanted to get better so she could go to college and become a doctor. She said: "I want to help people who are suffering like me."

Antiquated medical equipment, unreliable electricity

Each trip, the team has to deliver medicine to more than 1,500 patients like Yongsim within 21 days.

Packing for a medical operation of this size is daunting. The tuberculosis centres have unstable electricity and running water, so in addition to the boxes of medicine, we carried our own generators. We also brought modern diagnostic machines.

At a couple of centres, I was shown fluoroscopy (X-ray) machines from the 1950s that were still being used.

Many of the centres were spread out in remote locations and that often meant driving our loaded vans on unpaved roads for hours. "It's like being thrown around in a washing machine," one of the volunteers joked, making our North Korean guides laugh.

I had plenty to observe during these long drives, often noticing interesting contrasts such as militant propaganda signs set in tranquil countryside.

I will never forget the first tuberculosis centre I visited. As our vans pulled into the driveway, I saw more than 100 patients and staff waiting for us in the yard. As soon as we stopped, the North Korean medical team rushed over with huge smiles.

I realised I was witnessing a reunion of old friends who had been working towards the same goal for decades.

As I watched the two sides ask each other how they had been for the past six months, chatting about who got married and who had babies, I discarded any assumptions I might have had about the North Korean people.

The genuine concern the Eugene Bell team had for their patients was evident as well. Their greetings were often followed by an anxious scan of the patients and a pressing question — "Have we lost anyone?"

Remarkable achievements despite difficult conditions

Despite formidable challenges, the Eugene Bell Foundation and the North Korean doctors have together helped treat more than 3,000 MDR-TB patients, with a 75 per cent cure rate. It is a remarkable achievement, considering the global average cure rate remains at 45 per cent.

Heartbreaking cases are still too frequent though, like the patient who biked for two days, desperate to reach the only place he might receive treatment, or a skeletal patient so agonisingly short of breath that he could only take a few steps before resting.

Documentary filmmaker Hein S Seok. ( Supplied: Hein S Seok )

I have filmed North Koreans at their most vulnerable, but also at their most compassionate. Despite having to work with antiquated equipment and scant medical supplies, many doctors and nurses told me they found their calling at the tuberculosis centres.

My journey through North Korea was sometimes nerve-racking due to political tensions and the ever-present risk of infection. But I am privileged. I became a small part of one of the most incredible bonds I have ever witnessed, one between people from countries that are still technically at war, and that have been built one visit at a time, six months apart, for 20 years and counting.

Dr Linton was right. What I thought I knew before was not at all what I ended up finding.

Out of Breath airs on Foreign Correspondent on ABC TV at 8:00pm Tuesday, February 19.