1. Department of Infectious Diseases, Istituto Superiore di Sanità, Rome, Italy.
2. National HIV/AIDS Research Center, Istituto Superiore di Sanità, Rome, Italy.
3. Infectious Diseases Unit, Department of Public Health and Infectious Disease, Sapienza University of Rome, Rome, Italy.
4. Unit of Clinical Laboratory Science, Department of Medicine, Università Campus Bio-Medico Rome, Rome, Italy.
5. Theoretical Biology and Biophysics Group, Los Alamos National Laboratory, Los Alamos, New Mexico.