West Nile virus outbreak in humans, Greece, 2012: third consecutive year of local transmission

In 2010, the first outbreak of West Nile virus (WNV) infection in Greece was recorded, the largest in Europe since 1996. After 2010, outbreaks continued to occur in different areas of the country. Enhanced surveillance was implemented during transmission periods (June to October). We investigated the 2012 outbreak to determine its extent and identify risk factors for severe disease using regression models. Of 161 cases recorded in 2012, 109 had neuroinvasive disease (WNND). Two outbreak epicentres were identified: the southern suburbs of Athens in July and a rural area in East Macedonia &Thrace in August-September. The case fatality rate of the WNND cases was 17% (18/109). A lower case fatality rate was recorded in the two epicentres (7% (2/28) and 9% (4/46)): the higher case fatality outside the two epicentres might reflect a diagnostic bias. Age above 74 years (adjusted risk ratio (RR): 7.0; 95% CI: 2.2-22) and chronic renal failure (adjusted RR: 4.5; 95% CI: 2.7-7.5) were independently associated with WNND-related death. In three PCR-positive samples, sequencing revealed WNV lineage 2 identical to the 2010 strain. The occurrence of human cases in three consecutive years suggests that WNV lineage 2 has become established in Greece. Raising awareness among physicians and susceptible populations (elderly people and persons with comorbidities) throughout Greece is critical to reduce the disease impact.