Dengue subclinical infection an antecedent to secondary Dengue

Dengue is a major public health problem. The severity of Dengue infection depends on serotype of infecting virus, previous exposure of the patient to Dengue virus and age of the patient. Though most of the infections have a subclinical course, Dengue differs from them in causing a more severe and fatal infection instead of being protective during subsequent infections. This has been attributed to the immunological enhancement. Mild and sub-clinical infections go unnoticed and unreported. Thus this study is focused on screening the family members of the Dengue infected cases for subclinical infection.This study was done over a period of 3 months. Blood samples from 102 asymptomatic family members of 51 laboratory confirmed cases of Dengue were screened for Dengue IgM and IgG by immunocapture ELISA on day 7 of identifying a case. WBC and platelet counts were done both in cases and asymptomatic family members. The subjects who were found to have Dengue IgM were tested for IgG antibody on day 14. On Day 7, out of 102 subjects screened, 34 were positive for Dengue IgM and negative for IgG, 4 were positive for both IgM and IgG antibodies and 4 were positive for IgG alone. Leukocyte and platelet counts of these 42 subjects were normal. 3434 subjects were positive for IgG antibody on day 14. The highest percentage of subclinical infection was found in the age group of 2 to 4 years. There is a 37.3 prevalence of subclinical Dengue infection among the asymptomatic family members of the Dengue confirmed cases screened. The younger children showed a higher percentage of subclinical infection than older children. Mere presence of IgM antibody is not sufficient for the diagnosis of Acute Dengue. The importance has to be laid on the clinical presentation and blood counts in the diagnosis of Dengue because Dengue antibodies are produced in subclinical cases also. The knowledge of prevalence of subclinical infection also helps in suspecting secondary Dengue infection even if patients present for the first time with symptoms suggestive of Dengue.