On choosing a key indicator for leprosy control

Leprosy Mailing List, April 11^th, 2009

 

Ref.:    On choosing a key indicator for leprosy control

From:  Velema J. P., Apeldoorn, The Netherlands

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Dear Salvatore,

 

In its meeting later this month, WHO will be discussing with ILEP and other partners the draft global strategy and draft operational guidelines for the years 2011-2015 for further reducing the disease burden due to leprosy.  In these drafts, the proposed new key indicator of success will be the rate of new cases with grade-2 disabilities per 100,000 population per year.  The global target will be to reduce this rate by 50% in five years.

 

The rate of new cases with grade-2 disability is a combination of two already well-known indicators: the new case detection rate and the proportion of new cases with grade-2 disabilities (often mistakenly referred to as the ‘disability rate’).  The simple multiplication of these two indicators yields the rate of new cases with grade-2 disabilities.  Perhaps the NCG2-rate would be a helpful abbreviation of this term.

 

Making this choice focuses attention on that which is widely believed to make leprosy the problem that it is: the disability and disfigurement which result from nerve function impairment.  This target thus will support efforts to prevent disabilities among those affected by leprosy.

 

If we want to prevent grade-2 disabilities from occurring, we should either focus on early detection of leprosy – before nerves were impaired – or we should focus on detecting early signs of nerve function impairment (grade-1 disabilities) and take measures to either reverse these impairments or prevent them from deteriorating into visible deformities.

 

However, one can imagine a situation where new cases of leprosy are diagnosed but, through lack of training, time or interest, little attention is given to the diagnosis of nerve function impairments or deformities.  In such a situation, only the most obvious disabilities due to leprosy are detected while many less immediately visible impairments are missed. Underreporting is the result; the NCG2-rate would be low but would not be reflective of success.

 

A disadvantage is that in leprosy work we are not used to this new indicator.  Time will be needed for people to get a ‘feel’ for what are credible values and what represents a high or a low value.  For the proportion of new cases with grade-2 disabilities, we know that African countries generally have higher values than Asian countries, that a value higher than 10% is indicative of delayed case detection while a value of 1% or less means that leprosy-related disability is underreported.  Such simple reference values for the new indicator will have to be developed through experience in the next few years and it will take time for this knowledge to become generalised.

 

Besides the well-known new case detection rate, alternative indicators would include the rate of new cases of leprosy with grade-1 or grade- 2 disabilities at diagnosis.

 

I invite you, the reader, to think with me about these issues so that all aspects of the problem can come to the table and be taken into account when the final choice for a new target is made.

 

 

Dr. Johan P. Velema

Int'l Research & Development Officer

The Leprosy Mission International

P.O. Box 902 , 7301 BD Apeldoorn

The Netherlands