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Background & Objectives: Diagnosis of dengue infection is easily and best accomplished by demonstration of specific IgM antibodies in blood. We analyzed retrospectively the dengue IgM seropositivity available for samples obtained over a period of five year (1999-2003) from patients with suspected dengue fever (DF)-like illness to investigate whether there was an overall increase in the dengue IgM prevalence over this period., Methods: Serum samples from a total of 1426 individuals (suspected dengue cases) obtained over five year were tested for dengue specific IgM antibodies. Of the 1426 patients, 693 were adults (>15 yr) and 694 children (<15 yr) (excluding 39 individuals whose age was not known). There were 807 males and 610 females (excluding 9 individuals whose status on sex was unknown)., Results: A total of 423 (29.7%) samples were positive for dengue IgM over the five year period. Overall, there was a significant increase in the percentage of dengue IgM positive individuals over the this period (P<0.001). When the individuals were grouped into children (<15 yr) and adults (>15 yr), a significant increase in the number of dengue IgM positive individuals was noticed only in children (P<0.001) and not in adults. When the individuals were grouped into males and females, a significant increase in the number of dengue IgM positive individuals was noticed in both the sexes (P<0.03). Month-wise analysis of the dengue IgM positivity rates indicated the year-wide occurrence of dengue. A total of 158 (41%) of the dengue IgM positive individuals showed positivity for dengue IgG also suggestive of a secondary heterotypic infection., Interpretation & Conclusion: The overall significant increase in dengue IgM seropositivity among the suspected cases indicates an increase in dengue virus activity, raising the question whether dengue is emerging/re-emerging as a major health problem in southern India. Increase in probable secondary infection (as evidenced by dual positivity for dengue IgM and IgG) seen in this study is also a point of concern. Such an increase especially in a country like ours where multiple serotypes are prevalent, raises concern over probable increase in the incidences of the more serious DHF/DSS. As this report could well be an underestimate of true incidence, the alarming increase observed in 2003, may be a warning/indication of epidemics to come soon that merits serious consideration.