[1] Macfarlane Burnet Inst Med Res & Publ Hlth, Melbourne, Vic 3001, Australia
[2] Alfred Hosp, Infect Dis Unit, Melbourne, Vic, Australia
[3] Monash Univ, Prince Henrys Hosp, Dept Med, Melbourne, Vic 3004, Australia
[4] Johns Hopkins Univ, Dept Neurol, Baltimore, MD 21218 USA
[5] Johns Hopkins Univ, Dept Epidemiol, Baltimore, MD 21218 USA