Background: Kyasanur Forest Disease (KFD) is a zoonotic viral infection reported from India, with Shivamogga district consistently reporting a high burden. We conducted a case-control study in the outbreak-affected Thirthahalli block to identify risk factors for illness.

Methods: In the current 1:3 unmatched case-control study, a case was laboratory confirmed for KFD by IgM-ELISA or RTPCR, and a resident of Thirthahalli from January to May 2022. A control was defined as the absence of acute fever in a resident of Thirthahalli from January to May 2022. We identified cases from surveillance records. For each case, we selected controls randomly from the same and neighbouring hamlets. We collected data on sociodemographic parameters, risk factors and vaccination through interviews. We defined house conditions favouring tick bite exposure as regular tick sightings and storage of dry leaves or firewood collected from forests within house premises. We report an adjusted (aOR) odds ratio with 95% confidence intervals (CI).

Results: Among 25 cases (median age = 52 years, females = 52%; n=13) and 90 controls (median age = 49 years, females = 54%; n=49), demographic factors were comparable (p-value >0.05). Sixty-four per cent (n=16) cases were educated till the primary level as compared to 86% (n=77) controls (p-value <0.05). Monkey carcass sites within 500 m (aOR=7.2; 95% CI=1.5-34.4) and house conditions favouring tick bite exposure (aOR=3.4; 95% CI=1.2-9.7) were independent risk factors for illness. Being unvaccinated for KFD (aOR=1.3; 95% CI=0.5-3.7) was not significantly associated with illness.

Conclusions: We recommend strategies promoting prompt monkey carcass disposal, increasing awareness of the role of monkey carcasses in transmission and acaricidal spraying around monkey carcass sites and stores of dry leaves or firewood. Further studies should review the efficacy of the current vaccine formulation.