1. Monash University School of Public Health and Preventive Medicine, , Melbourne 3004 , Australia
2. The Alfred Hospital Department of Infectious Diseases, , Melbourne 3004 , Australia
3. The University of Queensland School of Public Health, , Brisbane 4006 , Australia
4. Royal Melbourne Hospital at the Peter Doherty Institute for Infection and Immunity Victorian Infectious Diseases Service, , Melbourne 3000 , Australia