Leprosy epidemiology and demographics
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Epidemiology and Demographics
Incidence
Although annual incidence—the number of new leprosy cases occurring each year—is important as a measure of transmission, it is difficult to measure in leprosy due to its long incubation period, delays in diagnosis after onset of the disease and the lack of laboratory tools to detect leprosy in its very early stages.
Worldwide, two to three million people are estimated to be permanently disabled because of Hansen's disease. India has the greatest number of cases, with Brazil second and Myanmar third.
In 1999, the world incidence of Hansen's disease was estimated to be 640,000; in 2000, 738,284 cases were identified. In 1999, 108 cases occurred in the United States. In 2000, the World Health Organization (WHO) listed 91 countries in which Hansen's disease is endemic.
India, Myanmar and Nepal contained 70% of cases. In 2002, 763,917 new cases were detected worldwide, and in that year the WHO listed Brazil, Madagascar, Mozambique, Tanzania and Nepal as having 90% of Hansen's disease cases.
According to recent figures from the WHO, new cases detected worldwide have decreased by approximately 107,000 cases (or 21%) from 2003 to 2004. This decreasing trend has been consistent for the past three years.
Prevalence
Registered prevalence is a useful proxy indicator of the disease burden as it reflects the number of active leprosy cases diagnosed with the disease and retrieving treatment with MDT at a given point in time.
The prevalence rate is defined as the number of cases registered for MDT treatment among the population in which the cases have occurred, again at a given point in time.[1]
New case detection is another indicator of the disease that is usually reported by countries on an annual basis. It includes cases diagnosed with onset of disease in the year in question (true incidence) and a large proportion of cases with onset in previous years (termed a backlog prevalence of undetected cases).
The new case detection rate (NCDR) is defined by the number of newly detected cases, previously untreated, during a year divided by the population in which the cases have occurred.
In addition, the global registered prevalence of HD was 286,063 cases; 407,791 new cases were detected during 2004.
Hansen's disease is tracked by the Centers for Disease Control and Prevention (CDC). Its prevalence in the United States is believed to be rising and underreported.[2] There are a rising number of cases worldwide, though pockets of high prevalence continue in certain areas such as Brazil, South Asia (India, Nepal), some parts of Africa (Tanzania, Madagascar, Mozambique) and the western Pacific.
As reported to WHO by 115 countries and territories in 2006, and published in the Weekly Epidemiological Record the global registered prevalence of leprosy at the beginning of the year was 219,826 cases. [3] New case detection during the previous year (2005 - the last year for which full country information is available) was 296,499. The reason for the annual detection being higher than the prevalence at the end of the year can be explained by the fact that a proportion of new cases complete their treatment within the year and therefore no longer remain on the registers. The global detection of new cases continues to show a sharp decline, falling by 110,000 cases (27%) during 2005 compared with the previous year.
| Table 1: Prevalence at beginning of 2006, and trends in new case detection 2001-2005, excluding Europe | ||||||
| Region | Registered Prevalence
(rate/10,000 pop.) |
New Case Detection during the year | ||||
|---|---|---|---|---|---|---|
| Start of 2006 | 2001 | 2002 | 2003 | 2004 | 2005 | |
| Africa | 40,830 (0.56) | 39,612 | 48,248 | 47,006 | 46,918 | 42,814 |
| Americas | 32,904 (0.39) | 42,830 | 39,939 | 52,435 | 52,662 | 41,780 |
| South-East Asia | 133,422 (0.81) | 668,658 | 520,632 | 405,147 | 298,603 | 201,635 |
| Eastern Mediterranean | 4,024 (0.09) | 4,758 | 4,665 | 3,940 | 3,392 | 3,133 |
| Western Pacific | 8,646 (0.05) | 7,404 | 7,154 | 6,190 | 6,216 | 7,137 |
| Totals | 219,826 | 763,262 | 620,638 | 514,718 | 407,791 | 296,499 |
Table 1 shows that global annual detection has been declining since 2001. The African region reported an 8.7% decline in the number of new cases compared with 2004. The comparable figure for the Americas was 20.1%, for South-East Asia 32% and for the Eastern Mediterranean it was 7.6%. The Western Pacific area, however, showed a 14.8% increase during the same period.
| Table 2: Prevalence and Detection, countries still to reach elimination | ||||||
| Countries | Registered Prevalence
(rate/10,000 pop.) |
New Case Detection
(rate/100,000 pop.) | ||||
|---|---|---|---|---|---|---|
| Start of 2004 | Start of 2005 | Start of 2006 | During 2003 | During 2004 | During 2005 | |
| Brazil | 79,908 (4.6) | 30,693 (1.7) | 27,313 (1.5) | 49,206 (28.6) | 49,384 (26.9) | 38,410 (20.6) |
| Democratic Republic of the Congo | 6,891 (1.3) | 10,530 (1.9) | 9,785 (1.7) | 7,165 (13.5) | 11,781 (21,1) | 10,737 (18.7) |
| Madagascar | 5,514 (3.4) | 4,610 (2.5) | 2,094 (1.1) | 5,104 (31.1) | 3,710 (20.5) | 2,709 (14.6) |
| Mozambique | 6,810 (3.4) | 4,692 (2.4) | 4,889 (2.5) | 5,907 (29.4) | 4,266 (22.0) | 5,371 (27.1) |
| Nepal | 7,549 (3.1) | 4,699 (1.8) | 4,921 (1.8) | 8,046 (32.9) | 6,958 (26.2) | 6,150 (22.7) |
| Tanzania | 5,420 (1.6) | 4,777 (1.3) | 4,190 (1.1) | 5,279 (15.4) | 5,190 (13.8) | 4,237 (11.1) |
| Totals | 112,092 | 60,001 | 53,192 | 80,707 | 81,289 | 67,614 |
Table 2 shows the leprosy situation in the six major countries which have yet to achieve the goal of elimination at the national level. It should be noted that: a) Elimination is defined as a prevalence of less than 1 case per 10,000 population; b) Madagascar reached elimination at the national level in September 2006; and c) Nepal detection reported from mid-November 2004 to mid-November 2005.
Due to the rising numbers, several support groups exist, the headquarters of which is currently in Lynbrook, NY and headed by Brian Marasco, leprosy survivor.
Endemic countries also report the number of new cases with established disabilities at the time of detection, as an indicator of the backlog prevalence. However, determination of the time of onset of the disease is generally unreliable, is very labour-intensive and is seldom done in recording these statistics.
Elimination of Leprosy as a Public Health Problem
In 1991 WHO's governing body, the World Health Assembly (WHA) passed a resolution to eliminate leprosy by the year 2000. Elimination of leprosy is defined as a prevalence rate of less than 1 case per 10 000 persons. The target was achieved on time and the widespread use of MDT reduced the disease burden dramatically.
- Over the past 20 years, more than 14 million leprosy patients have been cured, about 4 million since 2000.
- The prevalence rate of the disease has dropped by 90% – from 21.1 per 10 000 inhabitants to less than 1 per 10 000 inhabitants in 2000.
- Dramatic decrease in the global disease burden: from 5.2 million in 1985 to 805 000 in 1995 to 753 000 at the end of 1999 to 181 941 cases at the end of 2011.
- Leprosy has been eliminated from 119 countries out of 122 countries where the disease was considered as a public health problem in 1985.
- So far, there has been no resistance to antileprosy treatment when used as MDT.
- Efforts currently focus on eliminating leprosy at a national level in the remaining endemic countries and at a sub-national level from the others.
References
- ↑ "Epidemiology of leprosy in relation to control. Report of a WHO Study Group". World Health Organ Tech Rep Ser. 716: 1–60. 1985. PMID 3925646.
- ↑ Levis W (2007-05-20). "Leprosy rising". CNN.
- ↑ "Global leprosy situation, 2006" (PDF). Weekly Epidemiological Record. 81 (32): 309&ndash, 16. 2006.