Leprosy mailing
list – February 16th, 2005
Ccn:
all.
Ref.: morphological index (MI).
From: W van Brakel, Amsterdam, The Netherlands.
Dear Salvatore,
I would like to make a
small contribution to the BI/MI discussion on the list by challenging
the advantages of the MI you put forward.
1. checking that the
treatment is effective;
Does this
need checking? We know that MDT is highly effective, so why does this
need checking? Encouraging and monitoring treatment regularity of
patients under MDT would be much more useful, since smears are not
being repeated more than annually, if at all. The long-term
treatment efficacy of 12-month MB MDT is still under discussion,
particularly for highly smear-positive patients, but the efficacy will
need to be shown using the absence or presence of proven clinical
relapses as a criterion.
2. giving advice to the
patient about his/her risk to pass the infection to others (family
members, schoolmates, etc.);
This would
seem a very doubtful advice for several reasons:
1. M
leprae loose
viability more rapidly than MI-positivity.
2. Smears are
not repeated very frequently, if at all. How long should we wait to
inform a patient that he or she is no longer infectious? I would
advise health workers to encourage the patient at the start of MDT
that (s)he is no longer infectious after the first week of treatment.
3. The result
may be false positive. Do we know the inter-tester reliability of
MI reading? What is margin of error on an individual test? It could be
socially devastating to tell a person after taking MDT for one year,
based on a skin smear test with 1-2 apparently solid-staining bacilli
in an earlobe, that (s)he is still infectious!
3. detecting relapses.
The
relationship between MI-positivity ('viability' of bacilli) and
treatment efficacy or risk of relapse is not at all straightforward.
There are studies reporting people with solid-staining bacilli who
show no signs of relapse during many years of follow-up. Only if
smears have been documented to be repeatedly negative previously,
would a (
MI-
)positive smear be an indication of relapse. If the MI is useful at
all, it is probably as an aid in the diagnosis of relapse in a
patient with new clinical signs of leprosy or with a previously
negative BI.
With best
wishes,
Wim van
Brakel
Royal
Tropical Institute
Leprosy Unit
