Leprosy Mailing List – August 29, 2015
Ref.: (LML) Trend in the incidence rate of leprosy in India
From: Joey Almeida, India and UK
Dear Pieter,
With greater delay in detection of leprosy, more of the incident cases self-heal and fewer new cases are detected. However, undetected cases who fail to self-heal develop visible deformities at a steady rate.
Let:
NDDt be the annual number of newly detected cases with visible deformity at diagnosis in year t in a given geographical area,
PDANt be the proportion with visible deformity among the newly detected cases in year t in that area,
It be the incidence rate of leprosy cases in year t in that area.
Then,
NDDt is directly proportional to It and PDANt, respectively.
That is,
NDDt = k x It x PDANt
Where k is a constant
Therefore taking years a and b:
NDDa/NDDb = (k x Ia x PDANa)/(k x Ib x PDANb)
Rearranging and simplifying:
Ib/Ia = (NDDb/PDANb) / (NDDa/PDANa)
This equation can be used to determine whether the underlying incidence rate of leprosy in a given geographical area is changing over time.
Taking the reports from the Indian leprosy programme, between the years of 2008-9 and 2013-14, it can be shown that the incidence rate of leprosy in India is very unlikely to be declining, and could even be increasing.
Claims of a declining incidence rate of leprosy appear inconsistent with the evidence. Indians require earlier detection of leprosy and intensified anti-inflammatory protection against the avoidable nerve damage: during and after MDT.
Regards,
Joel Almeida
LML - S Deepak, B Naafs, S Noto and P Schreuder
LML blog link: http://leprosymailinglist.blogspot.it/
Contact: Dr Pieter Schreuder << editorlml@gmail.com
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