Serological Proficiency Tests for Dengue

Over the last 15 to 20 years, a gradual increase has been observed in the Americas in cases and epidemics of dengue and of dengue hemorrhagic fever (DHF) primarily due to: 1) geographical expansion and increase in densities of the Aedes aegypti mosquito; 2) circulation of several serotypes; 3) deterioration of vector control programs; 4) insufficient water supply; and other significant factors.

Considering the above, the countries, following the lead of the Pan American Health Organization (PAHO), have worked on developing active surveillance systems which are based on laboratory studies, making it possible to detect outbreaks and the introduction of new serotypes and to confirm cases of DHF, as well as other important aspects.

Currently, most countries have at least one laboratory where serological diagnosis of the disease is carried out (detection of IgM antibodies through IgM-capture ELISA, detection of total immunoglobulin through hemoagglutination inhibition and ELISA detection of IgG). Some countries have even developed laboratory networks. Several countries also have the capacity to isolate and detect dengue and the utilization of the polymerase chain reaction (PCR) technique is gradually being introduced as a rapid and relatively simple method for detecting the nucleic acid of the agent.

Due to expansion of the diagnosis of dengue, it has become necessary to periodically conduct proficiency tests in order to determine the quality of the diagnosis and to take the necessary measures for those cases that require them.

During 1996 and early 1997, the Virology Department of the Pedro Kouri Institute of Tropical Medicine, Collaborating Center of PAHO/WHO for the Study of Viral Diseases, was responsible, in coordination with PAHO, for organizing and developing the Serological Proficiency Tests for Dengue. To carry out the tests, initially panels of sera were prepared and sent to those laboratories in the region that had agreed to participate in the study.

Each laboratory received two panels, one for determining the presence of IgM antibodies and one for determining the titer of the hemoagglutination inhibiting antibodies. Each panel held 20 sera. To analyze the results obtained in each laboratory, the McNemar and Kappa tests were applied.

Of the twelve laboratories that participated in the study, six showed maximum concordance with regard to detection of IgM antibodies. Five showed variable but acceptable levels of concordance and only one showed unacceptable levels. Eight of the twelve participating laboratories carried out HI titration of antibodies to one or more dengue antigens in the corresponding panel of sera. Upon application of the Kappa test, only one laboratory showed poor concordance, and the others showed good to excellent concordance depending on the antigen processed.

The principal problem observed in the IgM-capture ELISA was detection of false negatives; the principal problem with HI was potentially inadequate titration of antigens. Most of the laboratories utilize antigens prepared in suckling mouse brain and extracted through the sucrose acetone method, usually obtained from one of the Collaborating Centers of PAHO/WHO in the Region.

Each laboratory was informed of its results, and pertinent recommendations were carried out where necessary.

The results obtained in the Serological Proficiency Tests suggest that for the most part serological diagnosis in the laboratories evaluated is of adequate quality. This type of study should serve as an incentive for other laboratories to take part in the Serological Proficiency Tests as a method of quality control for the diagnosis of dengue in the region and should be carried out periodically.

Table 1 shows the laboratories and countries participating in the study. As can be seen, participants included laboratories from countries with variable degrees of endemic dengue and from different areas in the region.

Table 1

            Serological Proficiency Tests for Dengue

 

INSTITUTION	COUNTRY
Dr. Julio I. Maiztegui National Institute of Human Viral Diseases	Argentina
CENETROP	Bolivia
Departmental Laboratory of Public Health, Antioquía	Colombia
Costa Rican Research and Teaching Institute in Nutrition and Health (INCIENSA)	Costa Rica
Dr. Defillo National Laboratory of Public Health	Dominican Republic
Leopoldo Izquieta Pérez National Institute of Hygiene and Tropical Medicine	Ecuador
National Institute of Epidemiological Diagnosis and Reference (INDRE)	Mexico
National Center for Diagnosis and Reference (CNDR)	Nicaragua
Gorgas Commemorative Center for Health Research and Information	Panama
National Institute of Health	Peru
Caribbean Epidemiology Centre (CAREC)	Trinidad and Tobago
Regional Laboratory for Diagnosis and Research on Dengue and other Viral Diseases (LARDIDEV)	Venezuela