1 Department of Molecular Medicine, "Microbiology and Virology" Unit, University Hospital "Policlinico Umberto I", Sapienza University, Rome, Italy. Electronic address: guido.antonelli@uniroma1.it.
2 Department of Biomedical and Biotechnological Sciences, Section of Microbiology, University of Catania, Catania, Italy.
3 Department of Translational Medicine and New Technologies in Medicine and Surgery, Retrovirus Centre, University of Pisa, "Clinical Virology Service," Pisa University Hospital, Pisa, Italy.