[1] Alfred Hosp, Dept Infect Dis & Microbiol, Melbourne, Vic 3181, Australia
[2] Monash Univ, Dept Med, Melbourne, Vic 3004, Australia
[3] Johns Hopkins Univ, Dept Neurol, Baltimore, MD 21218 USA
[4] Johns Hopkins Univ, Dept Epidemiol, Baltimore, MD 21218 USA