Changing proportions of paucibacillary leprosy cases in global leprosy case notification

Objectives:
Classification of new cases of leprosy into Paucibacillary (PB) or Multibacillary (MB) groups is important as it determines the duration of the treatment regimen, and predicts both complications of leprosy and risk of infection to contacts. Criteria have changed over the past 4 decades. We studied the published global leprosy statistics to reveal any major temporal changes in the proportion of PB cases.

Results:
Global data published by WHO over the past 40 years demonstrate a continuous decrease in the proportion of newly reported leprosy cases who are classified as paucibacillary (PB) from nearly 80% to around 40%. Independent validation of consistent and accurate classification is lacking.

Conclusions:
The decrease in PB proportion may be an artefactual, rather than an epidemiological, phenomenon. Whilst it is impossible to be certain, we suspect that a combination of changes in criteria and “overclassifying” to the MB group by field staff is the cause.