A dengue sero-prevalence study conducted amongst 5,236 children in the 9-12 years age group in three districts last year, as part of the first-ever multi-pronged epidemiological research study on dengue fever in Kerala, has revealed an overall sero-prevalence rate of 29%.
Dengue sero-prevalence was found to be as high as 41.2% amongst children in Thiruvananthapuram; Kollam, 24.2%; and Kozhikode, 25.9%. The three districts were the worst-affected in the previous dengue epidemic in the State in 2017
The dengue research study is a joint initiative of the State government and the World Health Organisation, with the Department of Community Medicine, Government Medical College, Thiruvananthapuram, as the nodal agency
The sero-prevalence survey is the first scientific attempt to estimate the actual community-level burden of dengue in the State.
Dengue sero-prevalence (detection of dengue-specific immunoglobulin G or IgG antibodies in blood samples) indicates the rate of previous dengue exposure and is an indicator of the intensity of dengue transmission in a community.
Nearly 80% of dengue infections are usually asymptomatic and these sub-clinical infections in the community go unnoticed.
The estimation of the actual dengue burdenin the community, through a sero-prevalence study, is crucial for evolving and implementing dengue control strategies.
Sero-prevalence is determined by measuring dengue antibody levels (IgG) in blood through Indirect IgG Elisa test. A positive test indicates the previous clinical or sub-clinical dengue infection the individual might have had.
As part of the study, blood samples collected from 5,236 children were studied. While the overall sero- positivity for dengue was found in 29% children, 68.7% was sero-negative for dengue. In about 2.2%, the tests came up as borderline or equivocal.
“As the age band goes up, dengue positivity will naturally go up. The sero-prevalence, if studied amongst adults, might be as high as 70%,” says P.S. Indu, Professor and Head, Community Medicine Department.
About 27.1% of the children in the survey or their families were unaware that they had already contracted dengue.
The high sero-positivity amongst children is a matter of concern as these children would be at risk of a much severe infection if during the next epidemic, another sero type of the dengue virus is dominant. (Dengue virus has four sero types and while DENV 1 and 2 are predominant in Kerala, all four sero types are circulating in the community).
WHO’s tool kit was used for estimating the disease burden.
A cross section of the serum samples were subjected to Dengue Plaque Reduction Neutralisation Test (PRNT) at the Rajiv Gandhi Centre for Biotechnology, one of the technical partners for the study, to assess the specificity and sensitivity of the Indirect IgG Elisa tests. RGCB has reported 87% concordance between PRNT and Indirect Elisa.
Dr. Indu said that as part of the research the children who were found to be dengue sero positive and sero negative would be followed-up for a specific period.
The Directorate of Health Services, the Departments of Microbiology and Paediatrics, GMCT; State Public Health Lab; and ICMR’s Vector Control Research Centre are also the technical collaborators in the study.
