Extensively drug-resistant tuberculosis (XDR-TB): the facts
MDR-TB:
MDR-TB is a laboratory diagnosis of resistance mycobacterium tuberculosis to INH and Rifampicin
XDR-TB:Currently defined as MDR-TB with further resistance to at least 3 of the 6 major classes of 2d line drugs.
http://www.doh.gov.za/docs/reports/2006/xdr/mxdr-tb.pdf
WORLD TB DAY 2007 | XDR-TB FACTSHEETA second way of developing MDR- or XDR-TB is
when a patient’s own TB develops resistance.
This can occur when anti-TB drugs are misused
or mismanaged. This happens when TB control
programmes are poorly managed, for example when
patients are not properly supported to complete
their full course of treatment; when health-care
providers prescribe the wrong treatment, or the
wrong dose, or for too short a period of time; when
the supply of drugs to the clinics dispensing drugs
is erratic; or when the drugs are of poor quality.
How easily is XDR-TB spread?There is probably 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 infectious
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 increases the longer
the time that a previously uninfected person spends
in the same room as an infectious 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
infectious patients receive 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% of affected people. But
successful outcomes also depend greatly on the
extent of the drug resistance, the 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 as soon as possible. Effective treatment
requires that all six classes of second-line drugs are
available to clinicians who have special expertise in
treating such cases.
How common is XDR-TB?We do not know at the moment, but XDR-TB is rare.
However, WHO estimates that there were almost
half a million cases of MDR-TB worldwide in 2004,
and MDR-TB usually has to occur before XDR-TB
arises.
We also know that findings from the only global
study carried out so far showed that in some places
perhaps as many as 19% of MDR-TB cases were
in fact XDR-TB, but this is likely to be uncommon.
Wherever second-line drugs to treat MDR-TB are
being misused, the possibility of XDR-TB exists.
Research is being carried out urgently to find out
more.
How can a person become infected withXDR-TB?The majority of healthy people with normal immunity
may never become ill with TB, unless they are
heavily exposed to infectious cases who are not
treated or who have been on treatment for less than
about one week.
Even then, 90% of people infected with TB
bacteria never develop TB disease. 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 becoming infected with TB is very low in
the open air. 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’ TB i.e drug-sensitive TB, avoidgetting XDR-TB?The most important thing is for a patient to continue
taking all their treatment exactly as 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, for example, the tablets make
them feel sick, they should inform their clinician or
nurse, 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.
Why have we never heard of XDR-TBbefore?For some years we have seen isolated cases of very
highly resistant TB around the world that we would
today call XDR-TB. All the drugs used against TB
have been around for a long time. If they are not
used carefully, then resistance can develop.
It is only recently, as we carry out regular surveys
of drug resistance in more and more countries, and
with improvements in laboratory capacity, that these
cases are being reported in greater numbers. This
has led to the problem being more closely examined
and given a name.
“WHO estimates that there were
almost half a million cases of MDR-TB
worldwide in 2004.”
