Global leprosy elimination: time to change more than the elimination target date.

espite the World Health Assem-bly's enthusiastic adoption in 1991 of a resolution to " eliminate leprosy as a public health problem by the year 2000 " , it remains an important cause of global chronic neurological disability. 1 The optimistic belief that leprosy could be conquered despite a limited understanding of its epidemiology was principally based on the availability of effective multidrug treatment (MDT), consisting of a combination of ri-fampicin, dapsone, and clofazimine. 2 3 For elimination purposes, " public health problem " was defined as less than one case of leprosy per 10 000 population the assumption being that below this prevalence level, loosely based on historical experience in Scandinavia and Western Europe, reduced transmission of Mycobacterium leprae would result in decreased incidence of infection and natural leprosy extinction. Disease prevalence was the measure chosen by the World Health Organisation (WHO) because of scepticism that incidence could be measured by routine surveillance systems due to leprosy's variable and comparatively long incubation period , the insidious onset of clinical disease, the tendency of many infected patients to self heal, and the chronic nature of disease. 4 The WHO is proud of the " success " of the leprosy elimination campaign. More than 10 million patients have received MDT therapy; the number of registered patients has decreased from 5 million in 1985 to less than a million in 2001; of 122 countries considered endemic in 1985, 107 have achieved the elimination target at country level; and by the end of 2000 the global prevalence of leprosy was reported as below 1 case per 10 000 population. 5 These accomplishments provided the impetus for extending the deadline for achieving the elimination goal at country level to 2005. How confident can we be that WHO's optimism is justified? The choice of prevalence as the measure for determining elimination is fundamentally flawed. The practice of reporting point prevalence at the end of a calendar year does not provide an accurate proxy of leprosy incidence or transmission , as it is dependent on the duration of infection, or in the case of the leprosy elimination campaign, the period that a patient remains on a treatment register. Thus, the cleaning of registers, removing patients that had died, been cured or been on treatment for indefinite prolonged periods, had a striking immediate effect on prevalence. However, the single greatest influence on prevalence was the WHO's decision to …