[1] Victorian Infect Dis Reference Lab, Div Epidemiol, Carlton, Vic 3053, Australia
[2] Victorian Infect Dis Reference Lab, Natl & Reg Polio Reference Lab, Melbourne, Vic, Australia
[3] Australian Paediat Surveillance Unit, Westmead, NSW, Australia
[4] Univ Sydney, Dept Paediat & Child Hlth, Sydney, NSW 2006, Australia