Tick-borne encephalitis: a retrospective study of clinical cases in Bornholm, Denmark.

Tick-borne encephalitis (TBE) is caused by a flavivirus, tick-borne encephalitis virus (TBEV). For decades TBE has been known to cause disease in Bornholm, a Danish island. A retrospective study was performed to identify undiagnosed cases of TBE among patients hospitalized with signs and symptoms of meningitis or encephalitis in the 5 y period 1994-1999. This investigation revealed 5 new, and initially undiagnosed cases of TBE. In total, 14 cases of TBE were found in the 7 y period 1994-2000; 2 patients were tourists and 12 cases were inhabitants in Bornholm, giving an incidence of 3.81 per 100,000 inhabitants. At least 5 patients (37.7%) had sequelae in concordance with the postencephalitic syndrome seen after TBE. In conclusion, the risk of being infected and developing TBE is still low among the population of Bornholm, but information about the disease and its sequelae is needed to form a basis for vaccination recommendations.