1 1st Division of Infectious Diseases, 'Luigi Sacco' University Hospital, Milan, Italy.
2 1st Division of Infectious Diseases, 'Luigi Sacco' University Hospital, Milan, Italy. Electronic address: amedeo.capetti@unimi.it.
3 Clinic of Infectious Diseases, DIBIC University of Milan, Italy.
4 1st Division of Infectious Diseases, 'Luigi Sacco' University Hospital, Milan, Italy; School of Medicine, University of the Witwatersrand, Johannesburg, South Africa.