Objective. Since 2005 there have been several reports of hepatitis B outbreak in the state of Kerala in southern India. Objective of this study was to analyze such outbreaks and to explore hypothesis pertaining the transmission mode. Methods. Retrospective observational study involving cases of acute hepatitis B acquired between 1 January 2015 and 31 December 2015 and their family members residing in Mazhuvanoor village in Ernakulam district of Kerala State in southern India. Results. 59 houses were included in the survey. The number of patients diagnosed to have acute viral hepatitis B was 59. Majority (66.10%) were over 50 years old. There were no cases below the age of 15 years. All 59 patients claimed to have been bitten frequently by a fly which was identified as “deer fly” belonging to the genus Chrysops. Conclusion. Given the current understanding of mechanical transmission of pathogens in both humans and animals by insects belonging to the Tabanidae family which also includes Chrysops, it is plausible that the same mechanism may hold true for hepatitis B also. However this needs to be proven in further studies both at the laboratory level and at field studies.