Detection of antibodies against TBE virus by means of western blot: Confirmation of a high level of false positive ELISA results in a population withlow TBE incidence

Former investigations comparing the anti-tick-borne encephalitis virus (TBE V) seroprevalence in risk-professions versus the general population in both the endemic region of southwestern Germany and the neighbouring North-East of France (Alsatia) revealed similar rates of seropositive individuals in both geographic areas. This was in discord with the known number of TEE pat ients: whereas up to 250 cases per year were observed in southwestern Germa ny, only about 30 patients were reported from the adjacent French region ov er the past 30 years. In order to exclude unspecific results in the ELISA testing, a Western blot method was established using highly purified TEE virus (strain K23) as ant igen. The method was evaluated on the one hand by means of known anti-TBEV- negative sera from healthy individuals and patients suffering from rheumati c disorders and, on the other, by using a seroconversion panel as well as s era from patients with known, clinically confirmed TBEV infection. After te st evaluation, ELISA-positive and ELISA-borderline sera of 248 German and 9 4 French individuals were retested by means of the Western blot method. Con sidering the ELISA-positive sera, 63.9% of the German (50.0% if only non-va ccinated individuals were considered) but only 10.5% of the French samples could be confirmed by Western blot. This difference in confirmation is high ly significant (p < 0.001). Among the ELISA-borderline sera, 97.4% of the G erman non-vaccinated sera and 100% of the French sera turned out to be nega tive in Western blot. The low confirmation rate of ELISA-positive or border line sera in the French sample indicates that the rate of naturally infecte d individuals in Alsatia is very low The ELISA method should be completed b y a confirmatory test with high specificity when samples collected from reg ions with unknown or low TEE incidence are studied.