-from Epidemiological
Bulletin , Vol. 25 No. 4, December 2004-
Rationale for surveillance
Lymphatic filariasis remains a major cause of overt or hidden clinical disease
in much of Asia, Africa, the Western Pacific and certain parts of the Americas.
It is the second leading cause of permanent long-term disability. The prevalence
is increasing world-wide, with at least 120 million people affected at different
stages of the disease. Both diethylcarbamazine (DEC) and ivermectin, given
as single doses, have been shown to be very effective in reducing microfilaraemia.
Filariasis was identified by the International Task Force on Disease Eradication as one of 6 potentially eradicable diseases. Current WHO policy is to achieve elimination of infection in humans mainly through combination drugs in large populations, complemented by antivector activities. Surveillance is therefore essential.
Recommended case definition
Clinical case definition
Hydrocoele, lymphoedema, elephantiasis or chyluria in a resident of an endemic
area for which other causes of these findings have been excluded.
Laboratory criteria for diagnosis
Microfilaria positive o sign of “dance” of the adult filarial on
ultrasound in the male genital area, antigen positive.
Case classification
Suspected: Not applicable.
Probable: A case that meets the clinical case definition.
Confirmed: A case with laboratory confirmation.
Recommended types of surveillance
There are currently three options and the choice will depend on the local situation:
• Routine monthly reporting of aggregated data on probable and confirmed
cases from periphery to intermediate level and to central level or
• Sentinel population surveys (standardised and periodical) or
• Active case finding through surveys of selected groups or through mass
surveys.
International: Annual reporting from central level to WHO (for a limited number of countries).
Recommended minimum data elements
Case-based data at peripheral level
Case classification (probable / confirmed).
Unique identifier.
Geographical information (location).
Laboratory result.
Aggregated data for reporting
Number of new cases.
Number of laboratory-confirmed cases.
Number of chronic conditions (hydrocoele, lymphoedema, elephantiasis or chyluria)
Recommended data analyses, presentation, reports
• Number of cases by geographical area and by year
• Monthly and yearly incidence, point prevalence (if active case detection),
by geographic origin, by sex, by parasitological diagnosis
In areas where a program based on universal treatment was initiated:
- Prevalence of microfilaremia/antigenemia in sentinel communities
Principal uses of data for decision-making
• Estimate the magnitude of the problem and define populations at risk
• Improve and focus the elimination activities
• Improve the management and follow-up of filariasis-infected patients
• Identify technical and operational difficulties
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Epidemiological
Bulletin , Vol. 25 No. 4, December 2004