The Australian state of Victoria is waking up to a seven-day "circuit-breaker" lockdown,
Twenty-six cases have been identified so-far, and a staggering 13,000 close or casual contacts have been identified and ordered to self-isolate.
Fears centre on at least two cases that were symptomatic but waited days to get a test.
Professor Catherine Bennett is a public health expert at Deakin University in Melbourne.
She spoke to Susie Ferguson.