Tick-borne encephalitis outbreak following raw goat milk consumption in a new micro-location, Croatia, June 2019

In June 2019, the Croatian Institute of Public Health was informed of a cluster of patients with laboratory confirmed tick-borne encephalitis (TBE) from the Gorski Kotar region. Five of the six patients with TBE reported consuming raw (unpasteurized) goat milk in the two week period before symptom onset, and one reported a recent tick bite. To assess risk factors for infection, we selected six control individuals from among healthy family and community members, and conducted a case-control analysis. None of the cases or controls were vaccinated against TBE. Individuals with TBE (cases) had 25 (95 % CI 0.8-1410.2, p = 0.021) times higher odds of raw goat milk consumption compared to healthy controls. Milk samples from 12 goats from the implicated farm were tested for the TBE virus (TBEV) using RT-PCR. TBEV RNA was not detected in the milk, but serological testing of goats and other farm animals yielded evidence of exposure to the virus: Six goats from the flock had TBEV neutralizing antibodies. Our findings suggest that the vehicle for the outbreak was raw goat milk from a single farm. Following public health advice to cease consumption of raw dairy products, no further cases have been reported.