No evidence of West Nile virus infection among Polish patients with encephalitis

West Nile virus (WNV) infection usually causes mild febrile illness, but in a small proportion of patients it can lead to encephalitis. Epidemiological studies of WNV indicate fast spread of infection worldwide and in Europe, but there have been no comprehensive studies of WNV infection among encephalitis patients in Poland. Here we present the results of WNV RNA and anti-WNV testing in serum and cerebrospinal fluid (CSF) samples in 80 patients with the clinical diagnosis of viral encephalitis. WNV RNA was not detected in any of the analyzed samples. Anti-WNV IgG and IgM were not present in CSF in any of the investigated patients, but anti-WNV IgM were unexpectedly detected in serum of 14 subjects. The latter represented false positive results are probably related to cross reactivity of antibodies. Although there was no evidence of WNV infection in any of our patients, epidemiological situation in the neighbouring countries warrants vigilance and appropriate measures, including introduction of specific diagnostic tools into clinical practice, seem necessary.