1 www.eurosurveillance.org Surveillance and outbreak reports West Nile virus outbreak in humans, Greece, 2012: third consecutive year of local transmission D Pervanidou (pervanidou@gmail.com) 1,2 , M Detsis 1 , K Danis 1,2 , K Mellou 1 , E Papanikolaou 1 , I Terzaki 1 , A Baka 1 , L Veneti 1 , A Vakali 1 , G Dougas 1 , C Politis 1 , K Stamoulis 3 , S Tsiodras 1,4 , T Georgakopoulou 1 , A Papa 5 , A Tsakris 4 , J Kremastinou 1 , C Hadjichristodoulou 1,6 1. Hellenic Center for Disease Control & Prevention, Athens, Greece 2. European Programme in Intervention Epidemiology Training (EPIET), European Centre for Disease Prevention and Control (ECDC), Stockholm, Sweden 3. Hellenic National Blood Centre, Athens, Greece 4. Medical Faculty, University of Athens, Athens, Greece 5. Medical Faculty, University of Thessaloniki, Thessaloniki, Greece 6. Medical Faculty, University of Thessaly, Larisa, Greece Citation style for this article: Pervanidou D, Detsis M, Danis K, Mellou K, Papanikolaou E, Terzaki I, Baka A, Veneti L, Vakali A, Dougas G, Politis C, Stamoulis K, Tsiodras S, Georgakopoulou T, Papa A, Tsakris A, Kremastinou J, Hadjichristodoulou C. West Nile virus outbreak in humans, Greece, 2012: third consecutive year of local transmission. Euro Surveill. 2014;19(13):pii=20758. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=20758 Article submitted on 09 July 2013 / published on 3 April 2014 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 surveil- lance 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 fail- ure (adjusted RR: 4.5; 95% CI: 2.7–7.5) were indepen- dently associated with WNND-related death. In three PCR-positive samples, sequencing revealed WNV lin- eage 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 suscepti- ble populations (elderly people and persons with co- morbidities) throughout Greece is critical to reduce the disease impact. Introduction West Nile virus (WNV) is one of the most widely dis- tributed arboviruses in the world, with endemic foci in Africa, the Middle East, west Asia, North and Central America, parts of Europe and Australia [1]. Human cases have been reported from several countries since the 1960s; however, the frequency of reported out- breaks has increased over the last 15–20 years [2,3]. About 20% of persons infected with WNV develop a mild disease, usually referred to as West Nile fever (WNF). In less than 1% of the cases, the virus causes a neuroinvasive disease (WNND) with serious neuro- logical manifestations, i.e. encephalitis, meningitis, meningoencephalitis or acute flaccid paralysis [4]. Among patients with severe illness, the case fatal- ity rate varies (e.g. approximately 10% in the United States [5] and 12–18% during transmission periods during 2010 to 2011 in Greece [6]). Two main WNV genetic lineages are known: lineage 1, identified in the majority of the outbreaks in humans and horses in Europe and the United States and line- age 2, which until 2004 had not been detected outside Africa, but since then has repeatedly appeared – ini- tially in Hungary in 2004 [7] and 2005–09 [8], in Russia in 2007 [9] and in Austria in 2008–09 [8,10]. Before 2010, symptomatic human cases of WNV infec- tion had not been documented in Greece. However, serosurveys in the early 60s, 80s and in 2007 suggest that WNV or a related flavivirus had been circulating at low levels in Greece at least since the 60s [11-13]. The first recorded outbreak of WNV infection in Greece was in 2010: this was the largest reported outbreak in Europe since 1996 [14], with 262 recorded cases. Of these, 197 developed WNND, of whom 33 (17%) died [15]. A seroprevelence study conducted after the 2010 outbreak (between 25 November to 22 December 2010) indicated that 1 in 140 people infected with WNV devel- oped WNND [16]. The outbreak in 2010 was first detected in the Central Macedonia region, in northern Greece [15,17]. Surveillance in the blood donor population and post- transfusion information during the 2010 outbreak