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, especially when administered together, or singly with a single dose of albendazole.
Because of highly effective diagnostic and treatment tools, 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 single-dose drug combinations administered once a year to all 'at risk' populations. Management of disease induced by lymphatic damage from the infection (especially elephantiasis and genital damage) is the second essential element in WHO policy. Surveillance is essential to identify previously undetected foci of infection and to monitor the reduction of microfilariae resulting from elimination efforts.
RECOMMENDED CASE DEFINITION
Clinical case definition
Hydrocoele or lymphoedema in a resident of an endemic area for which other causes of these findings have been excluded.
Laboratory criteria for diagnosis
Microfilaria positive, antigen positive or biopsy positive.
Suspected: Not applicable.
Probable: A case that meets the clinical case definition.
Confirmed: A person with laboratory confirmation even if he/she does not meet the clinical case definition.
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 (standardized 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 or lymphoedema)
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
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
See Regional Communicable Disease contacts on section "Communicable disease contacts in Regional Offices".
Headquarters: 20 Avenue Appia, CH-1211 Geneva 27, Switzerland
Eradication and Elimination of Diseases (CEE/CDS)/Lymphatic Filariasis
Elimination Project (FIL)
E-mail: email@example.com / Surveillancekit@who.ch
Tel: (41 22) 791 3225/2726/2111
Fax: (41 22) 791 4777