Benefit of detecting tick-borne encephalitis viremia in the first phase of illness

In Switzerland, reports of tick-borne encephalitis virus (TBEV) infections to the Federal Office of Public Health have increased by 100% in 2005 compared to the annual mean from 1999 to 2004. This might be partly due to unspecificity in serological testing. In order to make diagnostics more specific and to improve patient management, we recommend to consider the first phase of the biphasic course of TBE, that can be suspected in a trias of tick bite, followed by a feverish illness associated with thrombocytopenia and/or leucocytopenia. In this phase, detection of viremia by TBEV-specific polymerase chain reaction assay (PCR) will enable diagnosis as well as prediction of the second phase of TBEV infection, developing in the majority of patients. Circumstances suggesting detection of TBE viremia are exemplified by two case reports.