TB can become resistant to the two most powerful medicines that we have to treat it - isoniazid and rifampicin. If a TB infection is no longer able to be treated with either of these drugs, it is classed as multi-drug resistant TB.

Multi-drug resistant TB is a big problem. Normally treatment for TB is 90% effective, but with drug resistance, this effectiveness drops to as low as 50%. Extensively drug-resistant TB can occur if a person's TB is resistant to other second-line treatments as well as isoniazid and rifampicin. Only a third of people with extensively drug-resistant TB will be successfully cured.

Multi-drug resistant TB is more likely to develop when a person does not adhere to treatment. This can sometimes be a result of clinics not handling their care properly, for example, if they do not give the patient the medicines they need at the right time. It can also happen if an individual finds it hard to take the treatment.

Where drug-resistant TB is common in a community, it's possible to be infected with a strain of TB that's already got some resistance before you've started treatment.

Policymakers and healthcare professionals around the world are looking for ways to respond to the rise of multi-drug resistant TB. For now, the most important thing is that people take their treatment properly and receive proper support around adherence.    

Yes, the BCG vaccine can protect against TB. The vaccine is very effective against the most severe types of TB, offering up to 80% protection, however, protection against TB of the lungs is slightly lower.

Guidelines on who should be vaccinated will vary depending on where you are in the world. For countries with higher rates of TB, the World Health Organization recommends giving infants the BCG vaccine at birth. However, it's not recommended for babies who may be HIV-positive, as HIV-positive babies can develop a TB-like illness from the vaccine.

TB bacteria die slowly. To make sure that all the bacteria have gone you need to keep taking your medication as prescribed for the full length of time. You might start to feel better quite quickly, but you must keep taking your treatment until the end of the course.

If you don't finish all your medication or you take it irregularly, it can stop working. This is because if you haven't got enough of the medicine in your body, the bacteria will still be able to grow and will learn how to get past the medicine. This means that in the future your TB will be harder to treat. If your TB becomes resistant the chances of being cured will be smaller and you will have to take treatment for longer.

One way of helping people take their treatment regularly is 'directly observed therapy' (DOT). DOT is a way of taking treatment. It involves meeting with a health worker at a clinic, in the community or at home, for them to watch and make sure that you take your medicine correctly. It's a widely used approach to TB treatment and can be particularly helpful in cases where a person has difficulty in adhering to treatment.

DOT works best when healthcare workers use these meetings to provide patients with additional support. This could include helping them watch for side effects or providing counselling. The World Health Organization is currently exploring whether video calls could be used as a way of providing DOT in a more cost- and time-efficient way.