TB can usually be treated with a course of four standard, or first-line, anti-TB drugs. If these drugs are misused or mismanaged, then multi-drug resistant TB (MDR-TB) can develop. This takes longer to treat, with second-line drugs, which are more expensive and have more side effects.

XDR-TB can develop when these second-line drugs are also misused or mismanaged, and therefore also become ineffective. Because patients with XDR-TB are resistant to first- and second-line drugs, XDR-TB seriously limits treatment options. Therefore it is vital that TB control is managed properly.

What is MDR-TB?
MDR-TB or multidrug-resistant TB is a specific form of drug-resistant TB. This is when the TB bacteria are resistant to at least isoniazid and rifampicin, the two most powerful anti-TB drugs. XDR-TB is resistance to at least three of the six classes of available second-line drugs, in addition to MDR-TB.

How do you get XDR-TB?
People who are sick with TB in the lungs (the commonest site affected) are often infectious and can spread the disease by coughing, or sneezing, or simply talking, as this propels TB bacteria into the air. A person needs only to breathe in a small number of these germs to be infected. Sometimes the bacteria are already drug resistant if they come from a person who already has drug-resistant TB. There is a second way to develop MDR-TB or XDR-TB, and that is when a patient's own TB develops resistance. This can occur when anti-TB drugs are misused or mismanaged.

How easily is XDR-TB spread?
There is almost no difference between the speed of transmission of XDR-TB and any other forms of TB. The spread of TB bacteria depends on factors such as the number and concentration of contagious people in any one place together with the presence of people with a higher risk of being infected (such as those with HIV/AIDS). The risk of becoming infected goes up the longer the time that a previously uninfected person spends in the same room as the contagious case. The risk of spread increases where there is a high concentration of TB bacteria, such as can occur in closed environments like overcrowded houses, hospitals or prisons. The risk will be further increased if ventilation is poor. The risk of spread will be reduced and eventually eliminated if contagious patients are receiving proper treatment.

Can XDR-TB be cured or treated?
Yes, in some cases. Several countries, with good TB control programmes, have shown that cure is possible for up to 50-60 percent of affected people. But successful outcomes also depend greatly on the extent of the drug resistance, severity of the disease and whether the patient's immune system is compromised.

It is vital that clinicians caring for TB patients are aware of the possibility of drug resistance and have access to laboratories that can provide early and accurate diagnosis so that effective treatment is provided straight away.

How can a person avoid catching XDR-TB?
The majority of healthy people with normal immunity may never catch TB, unless they are heavily exposed to contagious cases who are not treated or who have been on treatment for less than about one week. Even then, 90 percent of people infected with TB bacteria never get the disease of TB. This applies to XDR-TB as well as to ordinary TB. People with HIV infection, however, in close contact with a TB patient, are more likely to catch TB and fall ill. The TB patients whom they meet should be encouraged to follow good cough hygiene, for example, covering their mouths with a handkerchief when they cough, or even, in the early stages of treatment, using a surgical mask, especially in closed environments with poor ventilation. The risk of getting infected with TB is very low outside in the open. Overall, the chances of being infected with XDR-TB are even lower than with 'ordinary' TB because cases of XDR-TB are still very rare.

How can a person who already has 'ordinary' i.e drug-sensitive TB, avoid getting XDR-TB?
The most important thing is for a patient to continue taking all their treatment exactly as it is prescribed. No doses should be missed, but this is especially important if the course of treatment is meant to be taken every other day - so-called 'intermittent treatment'. Above all, the treatment should be taken right through to the end. If a patient finds that side effects are a problem, then they should quickly discuss this with their clinicians, because often there is a very simple solution. If they need to go away for any reason, patients should make sure they have enough tablets with them for the duration of the trip.

What should be done if a person has been in contact with a known or suspect case of XDR-TB?
Anyone who has been in contact with someone known, or suspected to have XDR-TB, should consult their doctor, or a local TB clinic, and be screened to see if they have TB. This is most important if the person has any symptoms of TB.

If they have a cough, they will be asked to provide a sample of sputum which will be tested to see if there is any evidence of TB. Several other tests will be performed in the clinic including a skin test and a chest radiograph. If TB is found then treatment will be started with the drugs to which the person's TB is most likely to respond. If there is any evidence of infection with TB bacteria, but without disease, then preventive treatment may be given or, the person may simply be asked to attend regularly for a check up.

What risks are health workers facing with XDR-TB particularly those who may be HIV-positive themselves?
To protect health care workers who may come into contact with infectious TB patients, appropriate and strict infection control measures must be implemented in health care facilities at all times. Health care workers are also encouraged to make sure they are aware of their HIV status so that they can avoid putting themselves at risk of exposure.

How quickly can XDR-TB be diagnosed?
This depends on the access the patient has to health-care services. If TB bacteria are found in the sputum then the diagnosis of TB can be made in a day or two, but this finding will not be able to distinguish between drug-sensitive and drug-resistant TB. For this the bacteria in the sputum need to be grown in a laboratory. Final diagnosis in this way for TB and, especially for XDR-TB may take from 6 to 16 weeks. To reduce the time needed for diagnosis, new tools for rapid TB diagnosis are urgently needed.

Source: WHO Stop TB Department