Transmission study of dengue fever in Gampaha District, Sri Lanka

Abstract

RATIONALE: Dengue is an important flaviviral infection in Sri Lanka.OBJECTIVES; To determine the effect of possible contributing factors on transmission of Dengue METHODS: A total of 40 households situated around 7 selected dengue cases confirmed by both IgM-IgG ELISA and HAI assay were taken. A minimum of 3 inhabitants from each household were tested for anti-dengue antibodies. At each household, mosquito surveillance was carried out. RESULTS: Of the 40 households, 26(65%) were positive for dengue viral infection. Of the 148 inhabitants, 41 had evidence of exposure to dengue. Of the 41. asymptomatic dengue infection was observed in 25(61%). Paired sera were collected from 36/41 volunteers and tested by HAI assay which confirmed dengue virus infection in 4(11.1%) and were confirmed secondary. Three (75%) of them were asymptomatic. Balance 32(88.9%) was diagnosed as recent dengue infections. Of that 21(65.6%) were asymptomatic probable secondary 7(33.3%), recent dengue 14(66.6%)]. Clustering of cases was observed in all localities varying from 56.5%. There was a significant statistical association between the presence of a definitive dengue infection with the presence of Aedes vectors (x2=3.1, p=0.1). Ae. albopictus were found in all localities 'while Ae. aegypti was found only in one. Breteau index for Ae. albopictus varied from 0-260 while- container index varied from 0-84%. Highest clustering of dengue cases were observed in localities with the highest indices for' mosquitoes. CONCLUSIONS: Study confirms that the presence of asymptomatic infections and clustering of cases. The predominant vector was Ae. albopictus.