Tick-borne encephalitis diagnosis in patients with inflammatory changes in the cerebrospinal fluid in a region with very low prevalence.

Tick-borne encephalitis (TBE)-IgG antibodies are used for the serologic detection of antigen contact caused by TBE infection or immunization. In the present study, enzyme-linked immune sorbent assay (ELISA) results from a group of patients with inflammatory changes in the cerebrospinal fluid (CSF) were re-examined using Western blot technology. The result of the TBE-IgG-ELISA was positive in 47 of the 904 sera samples tested. Retesting the sera with a Western blot confirmed this result in only 31.8% of the positive cases. In 134 of the 904 sera, the ELISA result was borderline. In 5.5% of these sera, the Western blot reacted specifically. The remaining 723 sera samples tested negative with the ELISA. Of these sera, 15 were selected randomly and retested with the Western blot; none of them tested positive. The high number of false positive ELISA results can be explained by the highly selected group of patients and the low prevalence of TBE in the region studied. In patients with meningitis or encephalitis with positive ELISA results and uncharacteristic clinical symptoms, the treating physician should consider the possibility of nonspecific reactions involving inflammatory mediators or cross-reactivity with other flaviviruses. The ELISA-mediated diagnosis of TBE should therefore be verified by means of the patient's history and clinical symptoms, as well as further serologic tests including the Western blot, the hemagglutination test and the neutralization test.