Febrile illness is the most common reason for seeking healthcare in India and is associated with substantial morbidity and mortality. Dengue virus and Chikungunya Virus have recently shown an expanding range, moving from urban to rural areas, plains to hilly terrain, and continue to circulate endemically across tropical and subtropical regions worldwide.

The primary objectives are to determine the incidence of acute febrile illness, incidence, and seroprevalence of Dengue over a period of 12 months. Secondary objectives are to estimate the incidence and seroprevalence of chikungunya and to estimate the proportion of acute febrile illnesses caused by other common causes such as malaria, typhoid, leptospirosis, and scrub typhus.

Healthy individuals above 2 years of age from the Vellore HDSS area will be recruited in the study. 752 individuals with be enrolled in proportionate age bands in 5 clusters of 151 individuals each after informed consent if they fulfill all the inclusion criteria and none of the exclusion criteria. All these individuals will be followed up for 12 months from their date of enrolment. A baseline serosurvey for Dengue and Chikungunya will be performed and repeated at the end of the first year. During the follow-up period, all participants will be under weekly surveillance for the occurrence of fever. Any participant with a fever for more than two days will be visited and tested for dengue and chikungunya along with a complete blood count and rapid test for malaria. If the fever lasts for more than 10 days, tests for leptospira, typhoid, and scrub typhus will also be performed. All results will be provided to the participant. In the 3rd week after the onset of fever, convalescent serology will also be obtained for dengue and chikungunya. Apart from active surveillance, the participants can directly visit the study facility or telephonically contact the study team (passive surveillance). The economic burden due to dengue and chikungunya will also be analyzed.

Expected outcome:

We will be able to find the seroprevalence of dengue and chikungunya in the Vellore HDSS area and also the incidence of laboratory-confirmed dengue and chikungunya in those with acute febrile illness within the community.