1. Department of Infectious Diseases; The Second Affiliated Hospital of Medical School of Xi'an Jiaotong University; Xi'an Shaanxi China
2. Department of Epidemiology and Biostatistics; Medical School of Xi'an Jiaotong University; Xi'an Shaanxi China
3. Department of Infectious Diseases; Xi'an Children's Hospital of Medical School of Xi'an Jiaotong University; Xi'an Shaanxi China
4. Medical Research Council Human Immunology Unit; Weatherall Institute of Molecular Medicine; Oxford University; Oxford UK