Blood donation screening for West Nile virus (WNV) was mandatory in the Lazio region in 2017 and 2018 (June-November) according to the national surveillance plan. In these years, all five donations reactive in WNV nucleic acid amplification tests harboured instead Usutu virus (USUV). Clade 'Europe 2' was identified in four blood donations and a 2018 mosquito pool. The cocirculation of WNV and USUV in Lazio warrants increased laboratory support and awareness of possible virus misidentification.
Keywords: Flaviviridae; Italy; Usutu virus; West Nile virus; arbovirus; blood donation screening; blood-borne infections; emerging viruses; flavivirus; infection control; laboratory; surveillance; vector-borne infections; viral infections; zoonotic infections.