—from Epidemiological Bulletin, Vol. 23 No. 2, June 2002—
Case Definition
Leprosy
Rationale for surveillance
Leprosy continues to affect a large number of people. In 1997 there were
an estimated 1.5 million cases in the world. Control of the disease has improved
with the introduction of multidrug therapy (MDT). WHO has targeted the disease
for elimination (<1 case/10 000 population) by the year 2000, using a
focused flexible approach. This includes making multidrug therapy available
to all communities and areas, appropriate and good quality diagnosis and treatment,
with evaluation through epidemiological surveillance and programme monitoring.
Recommended case definition
Clinical description
The clinical manifestations of the disease vary in a continuous spectrum
between the two polar forms, lepromatous and tuberculoid leprosy:
- In lepromatous (multibacillary) leprosy, nodules, papules, macules and diffuse
infiltrations are bilateral symmetrical and usually numerous and extensive;
involvement of the nasal mucosa may lead to crusting, obstructed breathing and
epistaxis; ocular involvement leads to iritis and keratitis.
- In tuberculoid (paucibacillary) leprosy, skin lesions are single or few, sharply
demarcated, anaesthesic or hypoaesthesic, and bilateral asymmetrical, involvement
of peripheral nerves tends to be severe.
- Borderline leprosy has features of both polar forms and is more labile.
- Indeterminate leprosy is characterized by hypopigmented maculae with ill-defined
borders; if untreated, it may progress to tuberculoid, borderline or lepromatous
disease.
Laboratory criteria for confirmation
Alcohol-acid-fast bacilli in skin smears (made by the scrape-incision method).
In the paucibacillary form the bacilli may be so few that they are not demonstrable.
In view of the increasing prevalence of HIV and hepatitis B infection in many
countries where leprosy remains endemic, the number of skin smear sites and
the frequency of smear collection should be limited to the minimum necessary.
Case classification
WHO operational definition:
A case of leprosy is defined as a person showing one or more of the following
features, and who as yet has to complete a full course of treatment:
- hypopigmented or reddish skin lesions with definite loss of sensation
- involvement of the peripheral nerves, as demonstrated by definite thickening
with loss of sensation
- skin smear positive for acid-fast bacilli
Classification (microbiological):
Paucibacillary (PB): includes all smear-negative cases.
Multibacillary (MB): includes all smear-positive cases.
Classification (clinical):
Paucibacillary single lesion leprosy: 1 skin lesion.
Paucibacillary leprosy: 2 to 5 patches or lesions on the skin.
Multibacillary leprosy: >5 patches or lesions on the skin.
Recommended types of surveillance
Individual patient records at peripheral level for investigation and case-management.
Routine monthly reporting of aggregated data of all cases from periphery to intermediate level and from intermediate to central level.
International: Quarterly and annual reporting of aggregated
data from central level to WHO.
Recommended minimum data elements
Individual patient records
Unique identifier, name, sex, age, geographical information, disability
grade, laboratory examination, disease classification (multi- or paucibacillary,
see case definition), date treatment commenced, treatment outcome (disability,
cured, dropout), contacts.
Aggregated data for reporting – essential indicators (endemic
countries):
- Number of cases registered for treatment at a given time (usually end of year)
- Number of newly detected cases by type of leprosy
- Number of cases treated with multidrug therapy (MDT)
- Number of WHO grade 2 disability* among new cases
- Number of patients cured with MDT
- Number of relapses
*See: WHO technical Reports Series N°874, Geneva: World Health Organization, 1988: 31-32
Multidrug treatment (MDT) indicators (see special aspects)
MDT supply indicators:
For MB adult cases, MB child cases, PB adult cases, PB child cases:
- Number of patients under treatment
- Blister pack utilization (%)
Recommended data analyses, presentation, reports
Point prevalence, annual detection, MDT coverage, number of patients cured (wherever
possible based on cohort reporting), number of cases registered for chemotherapy
at the end of the year divided by the population in which the cases have occurred.
Graphs: Prevalence by year, detection by year, number of patients on multidrug therapy (MDT) by year, number of patients cured with MDT by year.
Maps: Number of registered cases, number of new cases, type of treatment, MDT coverage all by geographical area.
Tables: Prevalence, new case detection, percentage of children, percentage of disabled, percentage multibacillary, number of patients cured with MDT.
Principal uses of data for decision-making
- Assess the magnitude of the problem
- Identify variations in case-detection
- Evaluate the policy of elimination of leprosy
- Plan the distribution of drugs
- Identify technical and operational difficulties faced by the programme
- Identify high risk areas for further targeting intervention
- Evaluate impact of intervention
Special aspects
- Leprosy tends to be underreported. However, there are no reliable cost-effective
methods to estimate the real prevalence of the disease accurately.
- In endemic countries, essential indicators must be validated
through independent mechanisms in order to assess performance of MDT services
and progress towards the elimination of the disease at the local level.
Source: “WHO Recommended Surveillance Standards, Second edition, October
1999”, WHO/CDS/CSR/ISR/99.2
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Epidemiological Bulletin, Vol. 23 No. 2, June
2002