ethical clearance for the study was obtained from the faculty of medicine,University of paradeniya,Sri lanka. This was a retrospective study that analyzed the available data from Jaffna Teaching Hospital,which is the largest leading state hospital governed by the central Government of srilanka and is the only teaching hospital in the Northern province of srilanka. Altogether 2767 patients were admitted with a clinical diagnosis of DF between october 2009 and september 2010.However,complete data were available for only 1085 patients.