Tick-borne encephalitis in north-eastern Poland in 1997-2001: a retrospective study.

The aim of this study was to characterize the epidemiology and clinical features of tick-borne encephalitis in north-eastern Poland. Clinical and epidemiological data were analysed of patients hospitalized with the diagnosis in the Department of the Infectious Diseases and Neuroinfections of the Medical University in Bialystok in 1997-2001. Tick-borne encephalitis was diagnosed in 152 patients: 51 (34%) presented with meningitis, 89 (59%) with meningoencephalitis and 12 (8%) with meningoencephalomyelitis. Headache (84%) and fever (81%) were the most common symptoms. Meningeal signs were present in 137 patients (90%). Most common neurological abnormalities were: Oppenheim and Babinski signs (74 patients, 49%), ataxia (37, 24%), impaired consciousness (37, 24%) and pareses (16, 10%). Of patients examined, 146 (96%) had raised pleiocytosis, frequently accompanied by high cerebrospinal fluid protein concentration (90%), raised erythrocyte sedimentation rate (65%), peripheral blood leucocytosis (26%) and increased aminotransferase activity (16%). There was only 1 forest worker among the patients. Tick-borne encephalitis remains common in north-eastern Poland but, possibly because of effective vaccination, it has virtually disappeared among forest employees. The diagnosis appears difficult in some cases, as meningeal signs may not be present and laboratory findings may not be suggestive of a viral infection.