Vol. 17, No. 2	July 1996

During the International Course on Dengue and Dengue Hemorrhagic Fever in the Americas conducted at the "Pedro Kouri" Institute of Tropical Medicine (IPK) of Havana in August 1995, participants from 12 countries of the Region recommended standardization of the conditions for ELISA screening for detection of IgM antibodies to the dengue virus using blood samples taken on filter paper. The IPK, the Virology laboratories at the National Diagnosis and Reference Center (CNDR) of Nicaragua, the Costa Rican Institute for Research and Education in Nutrition and Health (INCIENSA), and PAHO decided to combine their efforts to provide a rapid response that would facilitate activities related to sero-epidemiological surveillance of dengue in Member Countries.

During the months of October and November 1995, two whole capillary blood samples were taken on filter paper (Blood Sampling Paper, NOBUTO, Tokyo Roshi Kaisha, Ltd. Japan) and serum from patients clinically suspected of having dengue was received through dengue surveillance in Costa Rica and Nicaragua. Cuban donor samples were also included. The samples taken on filter paper were kept at 4C and room temperature until processing. For each sample (serum and blood taken on filter paper) the presence of IgM antibodies was determined using the Dengue*IgM kit (IPK).

When the results obtained from sera and from samples taken on filter paper held for a period of 3 to 5 months at 4C were compared, sensitivity of 98.1%, specificity of 98.5% and coincidence of 98.3% were observed in 118 samples of each type processed. In 62 blood samples taken on filter paper and kept at room temperature for 3-5 months until processing, sensitivity of 94%, specificity of 100% and coincidence of 95.2% in comparison with the serum samples kept at 4C were observed. It is to be expected that samples kept at room temperature over a shorter period (15 days to a month) would show higher percentages for sensitivity and coincidence.

The results obtained make it possible to recommend the utilization of filter paper as a useful, simple and economic alternative for collection of blood samples for the serological surveillance of the dengue virus which does not require the collection of venous blood or the processing of blood to obtain the corresponding serum and facilitates shipment to the laboratory. It should be pointed out that the utilization of filter paper does not eliminate the need to collect serum samples useful for isolating and identifying the serotypes in circulation and for carrying out the genomic characterization of the strains present in the Region, studies that are of great interest in virological surveillance.

Source: Institute Pedro Kouri (IPK), Cuba; National Diagnosis and Reference Center (CNDR), Nicaragua; Costa Rican Institute for Research and Education in Nutrition and Health (INCENSA), Costa Rica.

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